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  <channel>
    <title>iOSDev.NYC</title>
    <description>A place to go for all iOS developers</description>
    <link>http://iosdev.nyc/</link>
    <atom:link href="http://iosdev.nyc/feed.xml" rel="self" type="application/rss+xml" />
    
      <item>
        <title>GitHub Pages and Automatic Deployment</title>
        <description>&lt;p&gt;In this post, I&amp;rsquo;ll help you set up automatic website deployment to free GitHub Pages hosting, using &lt;a href=&quot;http://www.wercker.com&quot;&gt;Wercker&lt;/a&gt; (also free!).&lt;/p&gt;

&lt;p&gt;Recently, my website was down for a few weeks, after I stopped &lt;a href=&quot;https://www.bitballoon.com/pricing&quot;&gt;BitBallon&lt;/a&gt; subscription. This time I wanted to try one of the free alternatives.&lt;/p&gt;

&lt;p&gt;I also wanted to learn something new in the process &amp;ndash; that&amp;rsquo;s why I didn&amp;rsquo;t want to use GitHub for building my Jekyll blog and that&amp;rsquo;s how I stumbled upon Wercker. &lt;/p&gt;

&lt;h1 id=&quot;build-your-website&quot;&gt;Build your website&lt;/h1&gt;

&lt;p&gt;I won&amp;rsquo;t cover building your website in details here. This is something requiring a separate post, or better, a series of posts, so I hope a website is something you already have.&lt;/p&gt;

&lt;p&gt;In my case, I&amp;rsquo;m using &lt;a href=&quot;https://jekyllrb.com&quot;&gt;Jekyll&lt;/a&gt; with &lt;a href=&quot;https://github.com/johnotander/pixyll&quot;&gt;Pixyll theme&lt;/a&gt;, with a few minor changes.&lt;/p&gt;

&lt;p&gt;If you&amp;rsquo;re not a fan of Jekyll, here&amp;rsquo;s a short list of some other frameworks I was considering:&lt;/p&gt;

&lt;ul&gt;
&lt;li&gt;&lt;a href=&quot;http://wintersmith.io&quot;&gt;http://wintersmith.io&lt;/a&gt;&lt;/li&gt;
&lt;li&gt;&lt;a href=&quot;http://assemble.io&quot;&gt;http://assemble.io&lt;/a&gt;&lt;/li&gt;
&lt;li&gt;&lt;a href=&quot;https://www.gatsbyjs.org&quot;&gt;https://www.gatsbyjs.org&lt;/a&gt;&lt;/li&gt;
&lt;li&gt;&lt;a href=&quot;https://hexo.io&quot;&gt;https://hexo.io&lt;/a&gt;&lt;/li&gt;
&lt;li&gt;&lt;a href=&quot;http://gohugo.io&quot;&gt;http://gohugo.io&lt;/a&gt;&lt;/li&gt;
&lt;/ul&gt;

&lt;h1 id=&quot;github-pages&quot;&gt;GitHub Pages&lt;/h1&gt;

&lt;p&gt;To host your website on GitHub pages, the easiets way is to create a repo named &lt;code&gt;YOUR-GITHUB-USERNAME.github.io&lt;/code&gt; and store your website on the master branch (you can &lt;a href=&quot;https://github.com/MariuszWisniewski/MariuszWisniewski.github.io&quot;&gt;see mine here&lt;/a&gt;).&lt;/p&gt;

&lt;p&gt;This is where Wercker will push your website after building it.&lt;/p&gt;

&lt;h1 id=&quot;wercker&quot;&gt;Wercker&lt;/h1&gt;

&lt;h2 id=&quot;build-website-script&quot;&gt;Build website script&lt;/h2&gt;

&lt;p&gt;First, prepare a piece of code which you will use to build your website as if you were building it for the first time. It might be only a one-liner, just write it down somewhere as we will use it in a minute.&lt;/p&gt;

&lt;p&gt;In my case (using Jekyll) it&amp;rsquo;s:&lt;/p&gt;
&lt;div class=&quot;highlight&quot;&gt;&lt;pre&gt;&lt;code class=&quot;language-bash&quot; data-lang=&quot;bash&quot;&gt;bundle install
&lt;span class=&quot;nv&quot;&gt;JEKYLL_ENV&lt;/span&gt;&lt;span class=&quot;o&quot;&gt;=&lt;/span&gt;production bundle &lt;span class=&quot;nb&quot;&gt;exec &lt;/span&gt;jekyll build --trace
&lt;/code&gt;&lt;/pre&gt;&lt;/div&gt;
&lt;blockquote&gt;
&lt;p&gt;I set jekyll environment variable here, which you might not need. My website behaves differently when it comes to analytics in development/production mode, so before building for deployment, I always switch to production.&lt;/p&gt;
&lt;/blockquote&gt;

&lt;h2 id=&quot;add-wercker-app&quot;&gt;Add Wercker app&lt;/h2&gt;

&lt;p&gt;Create an account on &lt;a href=&quot;http://www.wercker.com&quot;&gt;Wercker website&lt;/a&gt;. After you create it, it should ask you to create your first app. If it won&amp;rsquo;t, use this &lt;a href=&quot;https://app.wercker.com/applications/create&quot;&gt;create new app link&lt;/a&gt;.&lt;/p&gt;

&lt;p&gt;Choose where you keep your website source code (GitHub or BitBucket) and which access configuration you want (I went with the default one).&lt;/p&gt;

&lt;p&gt;Click finish (you don&amp;rsquo;t have to make your app public) and continue to configuring your workflow.&lt;/p&gt;

&lt;p&gt;You should end up on &lt;code&gt;Runs&lt;/code&gt; tab, which will be asking you to add &lt;code&gt;wercker.yml&lt;/code&gt; file to your repo.&lt;/p&gt;

&lt;p&gt;Here&amp;rsquo;s the one I used:&lt;/p&gt;
&lt;div class=&quot;highlight&quot;&gt;&lt;pre&gt;&lt;code class=&quot;language-bash&quot; data-lang=&quot;bash&quot;&gt;box: ruby
build:
  steps:
    &lt;span class=&quot;c&quot;&gt;# Go into site folder and install dependencies defined in Gemfile&lt;/span&gt;
    - script:
        name: Install bundle
        code: |
          bundle install

    &lt;span class=&quot;c&quot;&gt;# Set production environment and build&lt;/span&gt;
    &lt;span class=&quot;c&quot;&gt;# Generate the jekyll site with trace information on.&lt;/span&gt;
    &lt;span class=&quot;c&quot;&gt;# And store the result in the $WERCKER_OUTPUT_DIR, the&lt;/span&gt;
    &lt;span class=&quot;c&quot;&gt;# directory that is shared with the deployment pipeline.&lt;/span&gt;
    - script:
        name: Build Jekyll Page
        code: |
          &lt;span class=&quot;nv&quot;&gt;JEKYLL_ENV&lt;/span&gt;&lt;span class=&quot;o&quot;&gt;=&lt;/span&gt;production bundle &lt;span class=&quot;nb&quot;&gt;exec &lt;/span&gt;jekyll build --trace --destination &lt;span class=&quot;nv&quot;&gt;$WERCKER_OUTPUT_DIR&lt;/span&gt;

deploy:
  steps:
    - add-ssh-key:
        keyname: SSH_DEPLOY
        host: github.com
    - add-to-known_hosts:
        hostname: github.com
        fingerprint: 16:27:ac:a5:76:28:2d:36:63:1b:56:4d:eb:df:a6:48
    - leipert/git-push@0.7.6:
         host: github.com
         repo: username/username.github.io
         branch: master
         basedir: .
&lt;/code&gt;&lt;/pre&gt;&lt;/div&gt;
&lt;p&gt;(you can also &lt;a href=&quot;wercker.yml&quot;&gt;download the file here&lt;/a&gt;)&lt;/p&gt;

&lt;h3 id=&quot;wercker-configuration&quot;&gt;Wercker configuration&lt;/h3&gt;

&lt;p&gt;Let&amp;rsquo;s see how is the &lt;code&gt;wercker.yml&lt;/code&gt; config file built.   &lt;/p&gt;
&lt;div class=&quot;highlight&quot;&gt;&lt;pre&gt;&lt;code class=&quot;language-bash&quot; data-lang=&quot;bash&quot;&gt;box: ruby
&lt;/code&gt;&lt;/pre&gt;&lt;/div&gt;
&lt;p&gt;&lt;a href=&quot;http://devcenter.wercker.com/docs/boxes&quot;&gt;Box&lt;/a&gt; defines the name of the image that will be used for building your website. You can use any Docker image here, I went with standard &lt;code&gt;ruby&lt;/code&gt; image.&lt;/p&gt;

&lt;p&gt;We have two major steps:&lt;/p&gt;

&lt;ul&gt;
&lt;li&gt;build&lt;/li&gt;
&lt;li&gt;deploy&lt;/li&gt;
&lt;/ul&gt;

&lt;p&gt;They are connected to Pipelines, which you can find in Wercker under Workflows tab.&lt;/p&gt;

&lt;p&gt;&lt;img src=&quot;/images/posts/2017-11-20-wercker-github-pages/workflow_tab.png&quot; alt=&quot;Workflows Tab&quot;&gt;&lt;/p&gt;

&lt;p&gt;As you can see on the website, you have only &lt;code&gt;build&lt;/code&gt; pipeline in there. Scroll down and click &lt;code&gt;Add new pipeline&lt;/code&gt;.&lt;/p&gt;

&lt;p&gt;&lt;img src=&quot;/images/posts/2017-11-20-wercker-github-pages/new-pipeline.png&quot; alt=&quot;Add new pipeline&quot;&gt;&lt;/p&gt;

&lt;ul&gt;
&lt;li&gt;&lt;code&gt;Name&lt;/code&gt; &amp;ndash; Put here whatever you think best describes deployment phase;&lt;/li&gt;
&lt;li&gt;&lt;code&gt;YML Pipeline name&lt;/code&gt; &amp;ndash; This has to be the name of the pipeline as defined in &lt;code&gt;wercker.yml&lt;/code&gt; file. In the file I provided it&amp;rsquo;s called &lt;code&gt;deploy&lt;/code&gt; so put the same name in here. If you&amp;rsquo;d like to name it differently you can do so, just remember to also change pipeline name in &lt;code&gt;yml&lt;/code&gt; file;&lt;/li&gt;
&lt;li&gt;&lt;code&gt;Hook type&lt;/code&gt; &amp;ndash; choose &lt;code&gt;default&lt;/code&gt; which will allow chaining this pipeline after &lt;code&gt;build&lt;/code&gt; phase.&lt;/li&gt;
&lt;/ul&gt;

&lt;p&gt;Go back to Workflows tab and click plus button next to the &lt;code&gt;build&lt;/code&gt; pipeline in the Editor.&lt;/p&gt;

&lt;p&gt;&lt;img src=&quot;/images/posts/2017-11-20-wercker-github-pages/plus-button-build.png&quot; alt=&quot;Build plus button&quot;&gt;&lt;/p&gt;

&lt;p&gt;The only thing you should change now is &lt;code&gt;Execute pipeline&lt;/code&gt; &amp;ndash; click on the field, select &lt;code&gt;deploy&lt;/code&gt; and confirm by clicking &lt;code&gt;Add&lt;/code&gt;.&lt;/p&gt;

&lt;p&gt;&lt;img src=&quot;/images/posts/2017-11-20-wercker-github-pages/new-pipeline-workflow.png&quot; alt=&quot;Add deploy pipeline to Workflow&quot;&gt;&lt;/p&gt;

&lt;p&gt;This assures that our website is deployed automatically to GitHub Pages repo after each build.&lt;/p&gt;

&lt;h3 id=&quot;build-pipeline&quot;&gt;Build pipeline&lt;/h3&gt;

&lt;p&gt;&lt;em&gt;(I removed comments from the file below for clarity)&lt;/em&gt;&lt;/p&gt;
&lt;div class=&quot;highlight&quot;&gt;&lt;pre&gt;&lt;code class=&quot;language-bash&quot; data-lang=&quot;bash&quot;&gt;build:
  steps:
    - script:
        name: Install bundle
        code: |
          bundle install

    - script:
        name: Build Jekyll Page
        code: |
          &lt;span class=&quot;nv&quot;&gt;JEKYLL_ENV&lt;/span&gt;&lt;span class=&quot;o&quot;&gt;=&lt;/span&gt;production bundle &lt;span class=&quot;nb&quot;&gt;exec &lt;/span&gt;jekyll build --trace --destination &lt;span class=&quot;nv&quot;&gt;$WERCKER_OUTPUT_DIR&lt;/span&gt;
&lt;/code&gt;&lt;/pre&gt;&lt;/div&gt;
&lt;p&gt;As you can see, build pipeline steps are quite simple.&lt;/p&gt;

&lt;p&gt;We use custom scripts which consist of two parts &amp;ndash; script name that will be displayed on Wercker website during each pipeline phase and the code that will be executed.&lt;/p&gt;

&lt;p&gt;We have two scripts that could be easily combined into one, but in case of failure you will see what failed faster with separate steps.&lt;br&gt;
I used the script I asked you to prepare before, with just one small change &amp;ndash; as a build destination, we use &lt;code&gt;$WERCKER_OUTPUT_DIR&lt;/code&gt;, a variable that defines a folder that can be accessed also from &lt;code&gt;deploy&lt;/code&gt; pipeline.&lt;/p&gt;

&lt;p&gt;If you use anything else than Jekyll &amp;ndash; replace jekyll build command with anything else that builds your website. Just remember to use &lt;code&gt;$WERCKER_OUTPUT_DIR&lt;/code&gt; as a destination for the build process.&lt;/p&gt;

&lt;h3 id=&quot;deploy-pipeline&quot;&gt;Deploy pipeline&lt;/h3&gt;

&lt;p&gt;We will start from creating an &lt;code&gt;ssh key&lt;/code&gt; for deploying your website to GitHub pages.&lt;/p&gt;

&lt;p&gt;Go into Environment tab and click on &lt;code&gt;Generate SSH Key&lt;/code&gt;.&lt;/p&gt;

&lt;p&gt;&lt;img src=&quot;/images/posts/2017-11-20-wercker-github-pages/environment-tab.png&quot; alt=&quot;Environment tab&quot;&gt;&lt;/p&gt;

&lt;p&gt;&lt;img src=&quot;/images/posts/2017-11-20-wercker-github-pages/generate-ssh-key.png&quot; alt=&quot;Generate SSH Key&quot;&gt;&lt;/p&gt;

&lt;p&gt;As SSH Key name use &lt;code&gt;SSH_DEPLOY&lt;/code&gt; (the same name we used in &lt;code&gt;yml&lt;/code&gt; file), and click &lt;code&gt;Generate&lt;/code&gt;.&lt;/p&gt;

&lt;p&gt;&lt;img src=&quot;/images/posts/2017-11-20-wercker-github-pages/generate-ssh-key-name.png&quot; alt=&quot;New SSH Key&quot;&gt;&lt;/p&gt;

&lt;p&gt;Now you should see two positions under Environment tab:&lt;/p&gt;

&lt;ul&gt;
&lt;li&gt;&lt;code&gt;SSH_DEPLOY_PUBLIC&lt;/code&gt;&lt;/li&gt;
&lt;li&gt;&lt;code&gt;SSH_DEPLOY_PRIVATE&lt;/code&gt;&lt;/li&gt;
&lt;/ul&gt;

&lt;p&gt;Copy value under &lt;code&gt;SSH_DEPLOY_PUBLIC&lt;/code&gt; (it starts with &lt;code&gt;ssh-rsa&lt;/code&gt;) and go to your GitHub Pages repo prepared before (the one named &lt;code&gt;YOUR-GITHUB-USERNAME.github.io&lt;/code&gt;).&lt;/p&gt;

&lt;p&gt;Go into repository Settings and then to &lt;code&gt;Deploy keys&lt;/code&gt;.&lt;/p&gt;

&lt;p&gt;&lt;img src=&quot;/images/posts/2017-11-20-wercker-github-pages/github-go-to-deploy-keys.png&quot; alt=&quot;Go to GitHub Deploy Keys&quot;&gt;&lt;/p&gt;

&lt;p&gt;Add a new deploy key &amp;ndash; you can name it however you want, I used &lt;code&gt;wercker-deploy-key&lt;/code&gt; so I can remember later what it was created for. &lt;br&gt;
Remember to check &lt;code&gt;Allow write access&lt;/code&gt; box so Wercker can push to this repository. Into &lt;code&gt;Key&lt;/code&gt; field paste the value of &lt;code&gt;SSH_DEPLOY_PUBLIC&lt;/code&gt; key you copied from Wercker website.&lt;/p&gt;

&lt;p&gt;&lt;img src=&quot;/images/posts/2017-11-20-wercker-github-pages/paste-wercker-deploy-key.png&quot; alt=&quot;Add new deploy key&quot;&gt;&lt;/p&gt;

&lt;p&gt;Let&amp;rsquo;s get back to our &lt;code&gt;wercker.yml&lt;/code&gt; config file.&lt;/p&gt;
&lt;div class=&quot;highlight&quot;&gt;&lt;pre&gt;&lt;code class=&quot;language-bash&quot; data-lang=&quot;bash&quot;&gt;deploy:
  steps:
    - add-ssh-key:
        keyname: SSH_DEPLOY
        host: github.com
    - add-to-known_hosts:
        hostname: github.com
        fingerprint: 16:27:ac:a5:76:28:2d:36:63:1b:56:4d:eb:df:a6:48
    - leipert/git-push@0.7.6:
         host: github.com
         repo: username/username.github.io
         branch: master
         basedir: .
&lt;/code&gt;&lt;/pre&gt;&lt;/div&gt;
&lt;p&gt;We have 3 steps in here:&lt;/p&gt;

&lt;ol&gt;
&lt;li&gt;Adding an SSH key that will be used to push to your repo. We already created this key and added it to GitHub repository settings, so Wercker will be able to use it for pushing your website;&lt;/li&gt;
&lt;li&gt;Add to known hosts so Wercker environment will trust &lt;code&gt;github.com&lt;/code&gt; host&lt;/li&gt;
&lt;li&gt;&lt;a href=&quot;https://app.wercker.com/applications/53f202b50705e3656b000033/tab/details/&quot;&gt;Git-push&lt;/a&gt; (&lt;a href=&quot;https://github.com/leipert/step-git-push&quot;&gt;also on GitHub&lt;/a&gt;). All you have to do is replace &lt;code&gt;username&lt;/code&gt; with your actual username on GitHub. In my case this step looks like this:&lt;/li&gt;
&lt;/ol&gt;
&lt;div class=&quot;highlight&quot;&gt;&lt;pre&gt;&lt;code class=&quot;language-bash&quot; data-lang=&quot;bash&quot;&gt;    - leipert/git-push@0.7.6:
         host: github.com
         repo: MariuszWisniewski/MariuszWisniewski.github.io
         branch: master
         basedir: .
&lt;/code&gt;&lt;/pre&gt;&lt;/div&gt;
&lt;h1 id=&quot;summary&quot;&gt;Summary&lt;/h1&gt;

&lt;p&gt;That&amp;rsquo;s it! &lt;/p&gt;

&lt;p&gt;Now you can push a new commit to the repository where you host source code for your website (the one you linked in the &lt;a href=&quot;#add-wercker-app&quot;&gt;Add Wercker app&lt;/a&gt; step).&lt;/p&gt;

&lt;p&gt;Each new commit to this repo will build your website using the script provided in &lt;code&gt;build&lt;/code&gt; pipeline and will push it to GitHub Pages repository using &lt;code&gt;deploy&lt;/code&gt; pipeline.&lt;/p&gt;

&lt;p&gt;Let me know if you have any questions. In case of doubts, feel free to leave a comment!&lt;/p&gt;
</description>
        <pubDate>Mon, 20 Nov 2017 04:00:00 -0500</pubDate>
        <link>http://iosdev.nyc/blog/wercker-github-pages/</link>
        <guid isPermaLink="true">http://iosdev.nyc/blog/wercker-github-pages/</guid>
      </item>
    
      <item>
        <title>Credit Card Validation</title>
        <description>&lt;p&gt;When working on app recently, our payment processing provider, communicated to us that unfortunately they support only certain kinds of credit cards.&lt;/p&gt;

&lt;p&gt;We didn&amp;rsquo;t want to let users type card number that is not supported, only to send it to server, and after getting the response, show an error. &lt;/p&gt;

&lt;p&gt;If we know what types are supported, we can show the error earlier, and avoid sending any data &amp;ndash; making the experience much better for the user.&lt;/p&gt;

&lt;p&gt;We tried several frameworks but what we found is that:&lt;/p&gt;

&lt;ol&gt;
&lt;li&gt;most of the frameworks allow passing not correct CC number (e.g. Visa with 11 digits only validates just fine)&lt;/li&gt;
&lt;li&gt;all of the frameworks we tested, allow checking credit card type only after all digits are passed&lt;/li&gt;
&lt;/ol&gt;

&lt;p&gt;Especially 2. was imoportant for us to improve on. If we know e.g. that all Visa cards start with number 4, why wait until all 16 digits are typed?&lt;/p&gt;

&lt;p&gt;Same goes for cards that are not supported. If user types 34 in CC number field, we know it will be American Express card &amp;ndash; and if we don&amp;rsquo;t support it, we can immediately show the error.&lt;/p&gt;

&lt;p&gt;I described in more details what I created in a &lt;a href=&quot;https://medium.com/digitalforms/do-you-validate-credit-cards-in-your-ios-app-74d21e4f97a8&quot;&gt;Medium blog post&lt;/a&gt;, so please go there for more information. &lt;/p&gt;

&lt;p&gt;Or you can go directly to our &lt;a href=&quot;https://github.com/DigitalForms/CCValidator&quot;&gt;CCValidator framework GitHub page&lt;/a&gt;, and read installation and usage guide, or read short description below.&lt;/p&gt;

&lt;h3 id=&quot;installation-and-usage-guide&quot;&gt;Installation and usage guide&lt;/h3&gt;

&lt;p&gt;&lt;a href=&quot;https://github.com/DigitalForms/CCValidator&quot;&gt;CCValidator&lt;/a&gt; is available on &lt;a href=&quot;https://cocoapods.org/pods/CCValidator&quot;&gt;CocoaPods&lt;/a&gt; already.&lt;/p&gt;

&lt;p&gt;To install it, add to your Podfile:&lt;/p&gt;
&lt;div class=&quot;highlight&quot;&gt;&lt;pre&gt;&lt;code class=&quot;language-ruby&quot; data-lang=&quot;ruby&quot;&gt;&lt;span class=&quot;n&quot;&gt;pod&lt;/span&gt; &lt;span class=&quot;s1&quot;&gt;&#39;CCValidator&#39;&lt;/span&gt;&lt;span class=&quot;p&quot;&gt;,&lt;/span&gt; &lt;span class=&quot;s1&quot;&gt;&#39;~&amp;gt; 1.0&#39;&lt;/span&gt;
&lt;/code&gt;&lt;/pre&gt;&lt;/div&gt;
&lt;p&gt;Then, use it in your code:&lt;/p&gt;
&lt;div class=&quot;highlight&quot;&gt;&lt;pre&gt;&lt;code class=&quot;language-swift&quot; data-lang=&quot;swift&quot;&gt;&lt;span class=&quot;k&quot;&gt;let&lt;/span&gt; &lt;span class=&quot;nv&quot;&gt;recognizedType&lt;/span&gt; &lt;span class=&quot;o&quot;&gt;=&lt;/span&gt; &lt;span class=&quot;kt&quot;&gt;CCValidator&lt;/span&gt;&lt;span class=&quot;o&quot;&gt;.&lt;/span&gt;&lt;span class=&quot;nf&quot;&gt;typeCheckingPrefixOnly&lt;/span&gt;&lt;span class=&quot;p&quot;&gt;(&lt;/span&gt;&lt;span class=&quot;nv&quot;&gt;creditCardNumber&lt;/span&gt;&lt;span class=&quot;p&quot;&gt;:&lt;/span&gt; &lt;span class=&quot;n&quot;&gt;numberAsString&lt;/span&gt;&lt;span class=&quot;p&quot;&gt;)&lt;/span&gt;
&lt;span class=&quot;c1&quot;&gt;//check if type is e.g. .Visa, .MasterCard or .NotRecognized&lt;/span&gt;
&lt;/code&gt;&lt;/pre&gt;&lt;/div&gt;
&lt;p&gt;or if you don&amp;rsquo;t need credit card type, and need only to validate CC number correctness, use:&lt;/p&gt;
&lt;div class=&quot;highlight&quot;&gt;&lt;pre&gt;&lt;code class=&quot;language-swift&quot; data-lang=&quot;swift&quot;&gt;&lt;span class=&quot;k&quot;&gt;let&lt;/span&gt; &lt;span class=&quot;nv&quot;&gt;numberAsString&lt;/span&gt; &lt;span class=&quot;o&quot;&gt;=&lt;/span&gt; &lt;span class=&quot;n&quot;&gt;textField&lt;/span&gt;&lt;span class=&quot;o&quot;&gt;.&lt;/span&gt;&lt;span class=&quot;n&quot;&gt;text&lt;/span&gt;
&lt;span class=&quot;k&quot;&gt;let&lt;/span&gt; &lt;span class=&quot;nv&quot;&gt;isFullCardDataOK&lt;/span&gt; &lt;span class=&quot;o&quot;&gt;=&lt;/span&gt; &lt;span class=&quot;kt&quot;&gt;CCValidator&lt;/span&gt;&lt;span class=&quot;o&quot;&gt;.&lt;/span&gt;&lt;span class=&quot;nf&quot;&gt;validate&lt;/span&gt;&lt;span class=&quot;p&quot;&gt;(&lt;/span&gt;&lt;span class=&quot;nv&quot;&gt;creditCardNumber&lt;/span&gt;&lt;span class=&quot;p&quot;&gt;:&lt;/span&gt; &lt;span class=&quot;n&quot;&gt;numberAsString&lt;/span&gt;&lt;span class=&quot;p&quot;&gt;)&lt;/span&gt;
&lt;/code&gt;&lt;/pre&gt;&lt;/div&gt;
&lt;p&gt;Hope that&amp;rsquo;s gonna be useful for you. We will gladly welcome all contributions and ideas for what we should add to it!&lt;/p&gt;

&lt;p&gt;&lt;a href=&quot;https://github.com/DigitalForms/CCValidator&quot;&gt;https://github.com/DigitalForms/CCValidator&lt;/a&gt;&lt;/p&gt;
</description>
        <pubDate>Wed, 22 Feb 2017 04:00:00 -0500</pubDate>
        <link>http://iosdev.nyc/blog/credit-card-validation/</link>
        <guid isPermaLink="true">http://iosdev.nyc/blog/credit-card-validation/</guid>
      </item>
    
      <item>
        <title>Swifty function currying</title>
        <description>&lt;p&gt;Function currying is something I wanted to dig into for some time now, and finally I found a good time for it, especially now, after some &lt;a href=&quot;https://github.com/apple/swift-evolution/blob/master/proposals/0002-remove-currying.md&quot;&gt;changes introduced to the syntax&lt;/a&gt; in Swift 3. &lt;/p&gt;

&lt;h3 id=&quot;what-is-function-currying&quot;&gt;What is function currying?&lt;/h3&gt;

&lt;p&gt;What is &lt;code&gt;function currying&lt;/code&gt; (in general and in Swift)?&lt;/p&gt;

&lt;p&gt;If you want to get a full definition, see &lt;a href=&quot;https://en.wikipedia.org/wiki/Currying&quot;&gt;Wikipedia&lt;/a&gt;. In short, function currying lets us write code that translates a function taking two arguments, into a function taking one argument, and returning a function taking the next argument (and so on for 2, 3, 4, &amp;hellip; arguments).&lt;/p&gt;

&lt;p&gt;It might not sound super clear yet, so let&amp;rsquo;s take a look at some examples.&lt;/p&gt;
&lt;div class=&quot;highlight&quot;&gt;&lt;pre&gt;&lt;code class=&quot;language-swift&quot; data-lang=&quot;swift&quot;&gt;&lt;span class=&quot;kd&quot;&gt;func&lt;/span&gt; &lt;span class=&quot;nf&quot;&gt;multiplyTwoNumbers&lt;/span&gt;&lt;span class=&quot;p&quot;&gt;(&lt;/span&gt;&lt;span class=&quot;n&quot;&gt;_&lt;/span&gt; &lt;span class=&quot;nv&quot;&gt;a&lt;/span&gt;&lt;span class=&quot;p&quot;&gt;:&lt;/span&gt; &lt;span class=&quot;kt&quot;&gt;Int&lt;/span&gt;&lt;span class=&quot;p&quot;&gt;,&lt;/span&gt; &lt;span class=&quot;n&quot;&gt;_&lt;/span&gt; &lt;span class=&quot;nv&quot;&gt;b&lt;/span&gt;&lt;span class=&quot;p&quot;&gt;:&lt;/span&gt; &lt;span class=&quot;kt&quot;&gt;Int&lt;/span&gt;&lt;span class=&quot;p&quot;&gt;)&lt;/span&gt; &lt;span class=&quot;o&quot;&gt;-&amp;gt;&lt;/span&gt; &lt;span class=&quot;kt&quot;&gt;Int&lt;/span&gt; &lt;span class=&quot;p&quot;&gt;{&lt;/span&gt;
    &lt;span class=&quot;k&quot;&gt;return&lt;/span&gt; &lt;span class=&quot;n&quot;&gt;a&lt;/span&gt; &lt;span class=&quot;o&quot;&gt;*&lt;/span&gt; &lt;span class=&quot;n&quot;&gt;b&lt;/span&gt;
&lt;span class=&quot;p&quot;&gt;}&lt;/span&gt;

&lt;span class=&quot;nf&quot;&gt;multiplyTwoNumbers&lt;/span&gt;&lt;span class=&quot;p&quot;&gt;(&lt;/span&gt;&lt;span class=&quot;mi&quot;&gt;2&lt;/span&gt;&lt;span class=&quot;p&quot;&gt;,&lt;/span&gt; &lt;span class=&quot;mi&quot;&gt;3&lt;/span&gt;&lt;span class=&quot;p&quot;&gt;)&lt;/span&gt; &lt;span class=&quot;c1&quot;&gt;//result: 6&lt;/span&gt;
&lt;/code&gt;&lt;/pre&gt;&lt;/div&gt;
&lt;p&gt;Super simple, takes two Integers and returns result of their multiplication. What we have here is a 2 argument function that we will transform (as in definition), into function taking only one argument, returning another function, taking the second argument and returning an Integer.&lt;/p&gt;

&lt;p&gt;In pseudo-code it would be something like:&lt;/p&gt;
&lt;div class=&quot;highlight&quot;&gt;&lt;pre&gt;&lt;code class=&quot;language-&quot; data-lang=&quot;&quot;&gt;function(a, b) -&amp;gt; c
//into
function(a) -&amp;gt; (function(b) -&amp;gt; c)
&lt;/code&gt;&lt;/pre&gt;&lt;/div&gt;
&lt;p&gt;You could ask - how is that useful? Well, it allows for this newly created (curried) function to be evaluated over a period of time, with each call passing only a subset of the arguments (and saving each call result on the way if needed).&lt;/p&gt;

&lt;p&gt;So looking at our previous example, we could translate it into curried version like this:&lt;/p&gt;
&lt;div class=&quot;highlight&quot;&gt;&lt;pre&gt;&lt;code class=&quot;language-swift&quot; data-lang=&quot;swift&quot;&gt;&lt;span class=&quot;kd&quot;&gt;func&lt;/span&gt; &lt;span class=&quot;nf&quot;&gt;multiply&lt;/span&gt;&lt;span class=&quot;p&quot;&gt;(&lt;/span&gt;&lt;span class=&quot;n&quot;&gt;_&lt;/span&gt; &lt;span class=&quot;nv&quot;&gt;a&lt;/span&gt;&lt;span class=&quot;p&quot;&gt;:&lt;/span&gt; &lt;span class=&quot;kt&quot;&gt;Int&lt;/span&gt;&lt;span class=&quot;p&quot;&gt;)&lt;/span&gt; &lt;span class=&quot;o&quot;&gt;-&amp;gt;&lt;/span&gt; &lt;span class=&quot;p&quot;&gt;(&lt;/span&gt;&lt;span class=&quot;kt&quot;&gt;Int&lt;/span&gt;&lt;span class=&quot;p&quot;&gt;)&lt;/span&gt; &lt;span class=&quot;o&quot;&gt;-&amp;gt;&lt;/span&gt; &lt;span class=&quot;kt&quot;&gt;Int&lt;/span&gt; &lt;span class=&quot;p&quot;&gt;{&lt;/span&gt;
    &lt;span class=&quot;k&quot;&gt;return&lt;/span&gt; &lt;span class=&quot;p&quot;&gt;{&lt;/span&gt; &lt;span class=&quot;n&quot;&gt;b&lt;/span&gt; &lt;span class=&quot;k&quot;&gt;in&lt;/span&gt; &lt;span class=&quot;n&quot;&gt;a&lt;/span&gt; &lt;span class=&quot;o&quot;&gt;*&lt;/span&gt; &lt;span class=&quot;n&quot;&gt;b&lt;/span&gt; &lt;span class=&quot;p&quot;&gt;}&lt;/span&gt;
&lt;span class=&quot;p&quot;&gt;}&lt;/span&gt;

&lt;span class=&quot;nf&quot;&gt;multiply&lt;/span&gt;&lt;span class=&quot;p&quot;&gt;(&lt;/span&gt;&lt;span class=&quot;mi&quot;&gt;2&lt;/span&gt;&lt;span class=&quot;p&quot;&gt;)(&lt;/span&gt;&lt;span class=&quot;mi&quot;&gt;3&lt;/span&gt;&lt;span class=&quot;p&quot;&gt;)&lt;/span&gt; &lt;span class=&quot;c1&quot;&gt;//result: 6&lt;/span&gt;
&lt;/code&gt;&lt;/pre&gt;&lt;/div&gt;
&lt;p&gt;At this point, there&amp;rsquo;s still no real advantage, and we have this funky syntax, which is not obvious when you see it for the first time. But like I mentioned earlier, it allows us to evaluate it over time, and save each call result on the way. &lt;/p&gt;
&lt;div class=&quot;highlight&quot;&gt;&lt;pre&gt;&lt;code class=&quot;language-swift&quot; data-lang=&quot;swift&quot;&gt;&lt;span class=&quot;k&quot;&gt;let&lt;/span&gt; &lt;span class=&quot;nv&quot;&gt;multiplyBy10&lt;/span&gt; &lt;span class=&quot;o&quot;&gt;=&lt;/span&gt; &lt;span class=&quot;nf&quot;&gt;multiply&lt;/span&gt;&lt;span class=&quot;p&quot;&gt;(&lt;/span&gt;&lt;span class=&quot;mi&quot;&gt;10&lt;/span&gt;&lt;span class=&quot;p&quot;&gt;)&lt;/span&gt; 
&lt;span class=&quot;c1&quot;&gt;//result: function that will multiply its argument by 10&lt;/span&gt;

&lt;span class=&quot;k&quot;&gt;let&lt;/span&gt; &lt;span class=&quot;nv&quot;&gt;multiplyBy5&lt;/span&gt; &lt;span class=&quot;o&quot;&gt;=&lt;/span&gt; &lt;span class=&quot;nf&quot;&gt;multiply&lt;/span&gt;&lt;span class=&quot;p&quot;&gt;(&lt;/span&gt;&lt;span class=&quot;mi&quot;&gt;5&lt;/span&gt;&lt;span class=&quot;p&quot;&gt;)&lt;/span&gt; 
&lt;span class=&quot;c1&quot;&gt;//result: function that will multiply its argument by 5&lt;/span&gt;

&lt;span class=&quot;k&quot;&gt;let&lt;/span&gt; &lt;span class=&quot;nv&quot;&gt;multiplyBy2&lt;/span&gt; &lt;span class=&quot;o&quot;&gt;=&lt;/span&gt; &lt;span class=&quot;nf&quot;&gt;multiply&lt;/span&gt;&lt;span class=&quot;p&quot;&gt;(&lt;/span&gt;&lt;span class=&quot;mi&quot;&gt;2&lt;/span&gt;&lt;span class=&quot;p&quot;&gt;)&lt;/span&gt; 
&lt;span class=&quot;c1&quot;&gt;//result: function that will multiply its argument by 2&lt;/span&gt;
&lt;/code&gt;&lt;/pre&gt;&lt;/div&gt;
&lt;p&gt;Now you can call it like any other function:&lt;/p&gt;
&lt;div class=&quot;highlight&quot;&gt;&lt;pre&gt;&lt;code class=&quot;language-swift&quot; data-lang=&quot;swift&quot;&gt;&lt;span class=&quot;k&quot;&gt;let&lt;/span&gt; &lt;span class=&quot;nv&quot;&gt;x&lt;/span&gt; &lt;span class=&quot;o&quot;&gt;=&lt;/span&gt; &lt;span class=&quot;nf&quot;&gt;multiplyBy10&lt;/span&gt;&lt;span class=&quot;p&quot;&gt;(&lt;/span&gt;&lt;span class=&quot;mi&quot;&gt;2&lt;/span&gt;&lt;span class=&quot;p&quot;&gt;)&lt;/span&gt; &lt;span class=&quot;c1&quot;&gt;//result: 20&lt;/span&gt;
&lt;span class=&quot;k&quot;&gt;let&lt;/span&gt; &lt;span class=&quot;nv&quot;&gt;y&lt;/span&gt; &lt;span class=&quot;o&quot;&gt;=&lt;/span&gt; &lt;span class=&quot;nf&quot;&gt;multiplyBy5&lt;/span&gt;&lt;span class=&quot;p&quot;&gt;(&lt;/span&gt;&lt;span class=&quot;mi&quot;&gt;2&lt;/span&gt;&lt;span class=&quot;p&quot;&gt;)&lt;/span&gt; &lt;span class=&quot;c1&quot;&gt;//result: 10&lt;/span&gt;
&lt;span class=&quot;k&quot;&gt;let&lt;/span&gt; &lt;span class=&quot;nv&quot;&gt;z&lt;/span&gt; &lt;span class=&quot;o&quot;&gt;=&lt;/span&gt; &lt;span class=&quot;nf&quot;&gt;multiplyBy2&lt;/span&gt;&lt;span class=&quot;p&quot;&gt;(&lt;/span&gt;&lt;span class=&quot;mi&quot;&gt;2&lt;/span&gt;&lt;span class=&quot;p&quot;&gt;)&lt;/span&gt; &lt;span class=&quot;c1&quot;&gt;//result: 4&lt;/span&gt;
&lt;/code&gt;&lt;/pre&gt;&lt;/div&gt;
&lt;p&gt;If we wanted to achieve same thing without currying, we would have to write a new function, for every first argument combination, like this:&lt;/p&gt;
&lt;div class=&quot;highlight&quot;&gt;&lt;pre&gt;&lt;code class=&quot;language-swift&quot; data-lang=&quot;swift&quot;&gt;&lt;span class=&quot;kd&quot;&gt;func&lt;/span&gt; &lt;span class=&quot;nf&quot;&gt;multiplyBy10&lt;/span&gt;&lt;span class=&quot;p&quot;&gt;(&lt;/span&gt;&lt;span class=&quot;n&quot;&gt;_&lt;/span&gt; &lt;span class=&quot;nv&quot;&gt;a&lt;/span&gt;&lt;span class=&quot;p&quot;&gt;:&lt;/span&gt; &lt;span class=&quot;kt&quot;&gt;Int&lt;/span&gt;&lt;span class=&quot;p&quot;&gt;)&lt;/span&gt; &lt;span class=&quot;o&quot;&gt;-&amp;gt;&lt;/span&gt; &lt;span class=&quot;kt&quot;&gt;Int&lt;/span&gt; &lt;span class=&quot;p&quot;&gt;{&lt;/span&gt;
    &lt;span class=&quot;k&quot;&gt;return&lt;/span&gt; &lt;span class=&quot;n&quot;&gt;a&lt;/span&gt; &lt;span class=&quot;o&quot;&gt;*&lt;/span&gt; &lt;span class=&quot;mi&quot;&gt;10&lt;/span&gt;
&lt;span class=&quot;p&quot;&gt;}&lt;/span&gt;

&lt;span class=&quot;kd&quot;&gt;func&lt;/span&gt; &lt;span class=&quot;nf&quot;&gt;multiplyBy5&lt;/span&gt;&lt;span class=&quot;p&quot;&gt;(&lt;/span&gt;&lt;span class=&quot;n&quot;&gt;_&lt;/span&gt; &lt;span class=&quot;nv&quot;&gt;a&lt;/span&gt;&lt;span class=&quot;p&quot;&gt;:&lt;/span&gt; &lt;span class=&quot;kt&quot;&gt;Int&lt;/span&gt;&lt;span class=&quot;p&quot;&gt;)&lt;/span&gt; &lt;span class=&quot;o&quot;&gt;-&amp;gt;&lt;/span&gt; &lt;span class=&quot;kt&quot;&gt;Int&lt;/span&gt; &lt;span class=&quot;p&quot;&gt;{&lt;/span&gt;
    &lt;span class=&quot;k&quot;&gt;return&lt;/span&gt; &lt;span class=&quot;n&quot;&gt;a&lt;/span&gt; &lt;span class=&quot;o&quot;&gt;*&lt;/span&gt; &lt;span class=&quot;mi&quot;&gt;5&lt;/span&gt;
&lt;span class=&quot;p&quot;&gt;}&lt;/span&gt;

&lt;span class=&quot;kd&quot;&gt;func&lt;/span&gt; &lt;span class=&quot;nf&quot;&gt;multiplyBy2&lt;/span&gt;&lt;span class=&quot;p&quot;&gt;(&lt;/span&gt;&lt;span class=&quot;n&quot;&gt;_&lt;/span&gt; &lt;span class=&quot;nv&quot;&gt;a&lt;/span&gt;&lt;span class=&quot;p&quot;&gt;:&lt;/span&gt; &lt;span class=&quot;kt&quot;&gt;Int&lt;/span&gt;&lt;span class=&quot;p&quot;&gt;)&lt;/span&gt; &lt;span class=&quot;o&quot;&gt;-&amp;gt;&lt;/span&gt; &lt;span class=&quot;kt&quot;&gt;Int&lt;/span&gt; &lt;span class=&quot;p&quot;&gt;{&lt;/span&gt;
    &lt;span class=&quot;k&quot;&gt;return&lt;/span&gt; &lt;span class=&quot;n&quot;&gt;a&lt;/span&gt; &lt;span class=&quot;o&quot;&gt;*&lt;/span&gt; &lt;span class=&quot;mi&quot;&gt;2&lt;/span&gt;
&lt;span class=&quot;p&quot;&gt;}&lt;/span&gt;
&lt;/code&gt;&lt;/pre&gt;&lt;/div&gt;
&lt;p&gt;Much more writing, error-prone (most probably would implement it by copy-pasting) and when you know what function currying is, there&amp;rsquo;s no real difference in readablity (in my opinion).&lt;/p&gt;

&lt;h3 id=&quot;transforming-standard-functions-into-their-curried-versions&quot;&gt;Transforming standard functions into their curried versions&lt;/h3&gt;

&lt;p&gt;So far, we&amp;rsquo;ve been able to transform our own two-argument function into curried one. That&amp;rsquo;s quite easy, as we just rewrote it from scratch. Lets try to do something more complicated - tranform in a similar way UIColor.init(red: green: blue: alpha:) function, which we cannot modify directly in the source code.&lt;/p&gt;

&lt;p&gt;How can we create curried function out of one that&amp;rsquo;s not curried? We need to implement a function that takes an existing function as a parameter (the one we want to transform) and returns a curried wrapper around it.&lt;/p&gt;

&lt;p&gt;Before we go with UIColor&amp;rsquo;s init function, we will start by transforming our own multiplying function. To do this, we will create a function that takes (Int,Int)-&amp;gt;Int function as an argument and returns a curried wrapper around it.&lt;/p&gt;
&lt;div class=&quot;highlight&quot;&gt;&lt;pre&gt;&lt;code class=&quot;language-swift&quot; data-lang=&quot;swift&quot;&gt;&lt;span class=&quot;kd&quot;&gt;func&lt;/span&gt; &lt;span class=&quot;nf&quot;&gt;curriedVersion&lt;/span&gt;&lt;span class=&quot;p&quot;&gt;(&lt;/span&gt;&lt;span class=&quot;nv&quot;&gt;f&lt;/span&gt;&lt;span class=&quot;p&quot;&gt;:&lt;/span&gt; &lt;span class=&quot;kd&quot;&gt;@escaping&lt;/span&gt; &lt;span class=&quot;p&quot;&gt;(&lt;/span&gt;&lt;span class=&quot;kt&quot;&gt;Int&lt;/span&gt;&lt;span class=&quot;p&quot;&gt;,&lt;/span&gt; &lt;span class=&quot;kt&quot;&gt;Int&lt;/span&gt;&lt;span class=&quot;p&quot;&gt;)&lt;/span&gt; &lt;span class=&quot;o&quot;&gt;-&amp;gt;&lt;/span&gt; &lt;span class=&quot;kt&quot;&gt;Int&lt;/span&gt;&lt;span class=&quot;p&quot;&gt;)&lt;/span&gt; &lt;span class=&quot;o&quot;&gt;-&amp;gt;&lt;/span&gt; &lt;span class=&quot;p&quot;&gt;(&lt;/span&gt;&lt;span class=&quot;kt&quot;&gt;Int&lt;/span&gt;&lt;span class=&quot;p&quot;&gt;)&lt;/span&gt; &lt;span class=&quot;o&quot;&gt;-&amp;gt;&lt;/span&gt; &lt;span class=&quot;p&quot;&gt;(&lt;/span&gt;&lt;span class=&quot;kt&quot;&gt;Int&lt;/span&gt;&lt;span class=&quot;p&quot;&gt;)&lt;/span&gt; &lt;span class=&quot;o&quot;&gt;-&amp;gt;&lt;/span&gt; &lt;span class=&quot;kt&quot;&gt;Int&lt;/span&gt; &lt;span class=&quot;p&quot;&gt;{&lt;/span&gt;
    &lt;span class=&quot;k&quot;&gt;return&lt;/span&gt; &lt;span class=&quot;p&quot;&gt;{&lt;/span&gt; &lt;span class=&quot;n&quot;&gt;a&lt;/span&gt; &lt;span class=&quot;k&quot;&gt;in&lt;/span&gt; &lt;span class=&quot;p&quot;&gt;{&lt;/span&gt; &lt;span class=&quot;n&quot;&gt;b&lt;/span&gt; &lt;span class=&quot;k&quot;&gt;in&lt;/span&gt; &lt;span class=&quot;nf&quot;&gt;f&lt;/span&gt;&lt;span class=&quot;p&quot;&gt;(&lt;/span&gt;&lt;span class=&quot;n&quot;&gt;a&lt;/span&gt;&lt;span class=&quot;p&quot;&gt;,&lt;/span&gt;&lt;span class=&quot;n&quot;&gt;b&lt;/span&gt;&lt;span class=&quot;p&quot;&gt;)&lt;/span&gt; &lt;span class=&quot;p&quot;&gt;}&lt;/span&gt; &lt;span class=&quot;p&quot;&gt;}&lt;/span&gt;
&lt;span class=&quot;p&quot;&gt;}&lt;/span&gt;
&lt;/code&gt;&lt;/pre&gt;&lt;/div&gt;
&lt;hr&gt;

&lt;p&gt;&lt;em&gt;(What is &lt;code&gt;@escaping&lt;/code&gt; keyword? For more info I encourage you to visit &lt;a href=&quot;https://developer.apple.com/library/content/documentation/Swift/Conceptual/Swift_Programming_Language/Closures.html&quot;&gt;Apple docs&lt;/a&gt;, but in short &amp;ndash; we use it to mark a closure that will not be invoked directly by function taking this closure as an argument. In our case, we don&amp;rsquo;t call &lt;code&gt;f&lt;/code&gt; function directly, we just pass it around and return it to be called later)&lt;/em&gt;&lt;/p&gt;

&lt;hr&gt;

&lt;p&gt;As we see, our &lt;code&gt;curriedVersion&lt;/code&gt; function, takes as an argument a function (that matches &lt;code&gt;multiplyTwoNumbers&lt;/code&gt; signature) and returns a function, that returns a function, that returns an Integer (I know it might be hard to follow, but bare with me).&lt;/p&gt;

&lt;p&gt;Originally, our curried function &lt;code&gt;multiply&lt;/code&gt; returned a function, that took one argument and returned an Integer. Because we&amp;rsquo;re transforming a function here, we need a wrapper around it. Let&amp;rsquo;s take a look again at pseudo-code:&lt;/p&gt;

&lt;p&gt;&lt;strong&gt;Standard function&lt;/strong&gt; taking two arguments and returning a number&lt;/p&gt;
&lt;div class=&quot;highlight&quot;&gt;&lt;pre&gt;&lt;code class=&quot;language-&quot; data-lang=&quot;&quot;&gt;standardFunction = function(a,b) -&amp;gt; c
&lt;/code&gt;&lt;/pre&gt;&lt;/div&gt;
&lt;p&gt;&lt;strong&gt;Curried function&lt;/strong&gt; that takes one argument and returns a function taking second argument, and returning a number&lt;/p&gt;
&lt;div class=&quot;highlight&quot;&gt;&lt;pre&gt;&lt;code class=&quot;language-&quot; data-lang=&quot;&quot;&gt;curriedFunction = function(a) -&amp;gt; (function(b) -&amp;gt; c)
&lt;/code&gt;&lt;/pre&gt;&lt;/div&gt;
&lt;p&gt;How do we make &lt;code&gt;curriedFunction&lt;/code&gt; out of &lt;code&gt;standardFunction&lt;/code&gt;? We create a wrapper around it&lt;/p&gt;
&lt;div class=&quot;highlight&quot;&gt;&lt;pre&gt;&lt;code class=&quot;language-&quot; data-lang=&quot;&quot;&gt;transformingFunction = function(standardFunction) -&amp;gt; curriedFunction
&lt;/code&gt;&lt;/pre&gt;&lt;/div&gt;
&lt;p&gt;If we now substitute function names with their definitions we get&lt;/p&gt;
&lt;div class=&quot;highlight&quot;&gt;&lt;pre&gt;&lt;code class=&quot;language-&quot; data-lang=&quot;&quot;&gt;transformingFunction = function(function(a,b) -&amp;gt; c) -&amp;gt; function(a) -&amp;gt; (function(b) -&amp;gt; c)
&lt;/code&gt;&lt;/pre&gt;&lt;/div&gt;
&lt;p&gt;which looks similar to&lt;/p&gt;
&lt;div class=&quot;highlight&quot;&gt;&lt;pre&gt;&lt;code class=&quot;language-swift&quot; data-lang=&quot;swift&quot;&gt;&lt;span class=&quot;kd&quot;&gt;func&lt;/span&gt; &lt;span class=&quot;nf&quot;&gt;curriedVersion&lt;/span&gt;&lt;span class=&quot;p&quot;&gt;(&lt;/span&gt;&lt;span class=&quot;nv&quot;&gt;f&lt;/span&gt;&lt;span class=&quot;p&quot;&gt;:&lt;/span&gt; &lt;span class=&quot;kd&quot;&gt;@escaping&lt;/span&gt; &lt;span class=&quot;p&quot;&gt;(&lt;/span&gt;&lt;span class=&quot;kt&quot;&gt;Int&lt;/span&gt;&lt;span class=&quot;p&quot;&gt;,&lt;/span&gt; &lt;span class=&quot;kt&quot;&gt;Int&lt;/span&gt;&lt;span class=&quot;p&quot;&gt;)&lt;/span&gt; &lt;span class=&quot;o&quot;&gt;-&amp;gt;&lt;/span&gt; &lt;span class=&quot;kt&quot;&gt;Int&lt;/span&gt;&lt;span class=&quot;p&quot;&gt;)&lt;/span&gt; &lt;span class=&quot;o&quot;&gt;-&amp;gt;&lt;/span&gt; &lt;span class=&quot;p&quot;&gt;(&lt;/span&gt;&lt;span class=&quot;kt&quot;&gt;Int&lt;/span&gt;&lt;span class=&quot;p&quot;&gt;)&lt;/span&gt; &lt;span class=&quot;o&quot;&gt;-&amp;gt;&lt;/span&gt; &lt;span class=&quot;p&quot;&gt;(&lt;/span&gt;&lt;span class=&quot;kt&quot;&gt;Int&lt;/span&gt;&lt;span class=&quot;p&quot;&gt;)&lt;/span&gt; &lt;span class=&quot;o&quot;&gt;-&amp;gt;&lt;/span&gt; &lt;span class=&quot;kt&quot;&gt;Int&lt;/span&gt;
&lt;/code&gt;&lt;/pre&gt;&lt;/div&gt;
&lt;p&gt;Ok, so how do we use our transforming function? We just call it by passing to it our old &lt;code&gt;multiplyTwoNumbers&lt;/code&gt; function.&lt;/p&gt;
&lt;div class=&quot;highlight&quot;&gt;&lt;pre&gt;&lt;code class=&quot;language-swift&quot; data-lang=&quot;swift&quot;&gt;&lt;span class=&quot;k&quot;&gt;let&lt;/span&gt; &lt;span class=&quot;nv&quot;&gt;curriedMultiply&lt;/span&gt; &lt;span class=&quot;o&quot;&gt;=&lt;/span&gt; &lt;span class=&quot;nf&quot;&gt;curriedVersion&lt;/span&gt;&lt;span class=&quot;p&quot;&gt;(&lt;/span&gt;&lt;span class=&quot;nv&quot;&gt;f&lt;/span&gt;&lt;span class=&quot;p&quot;&gt;:&lt;/span&gt; &lt;span class=&quot;n&quot;&gt;multiplyTwoNumbers&lt;/span&gt;&lt;span class=&quot;p&quot;&gt;)&lt;/span&gt;
&lt;span class=&quot;nf&quot;&gt;curriedMultiply&lt;/span&gt;&lt;span class=&quot;p&quot;&gt;(&lt;/span&gt;&lt;span class=&quot;mi&quot;&gt;2&lt;/span&gt;&lt;span class=&quot;p&quot;&gt;)(&lt;/span&gt;&lt;span class=&quot;mi&quot;&gt;3&lt;/span&gt;&lt;span class=&quot;p&quot;&gt;)&lt;/span&gt;
&lt;/code&gt;&lt;/pre&gt;&lt;/div&gt;
&lt;h3 id=&quot;transforming-uicolor-init-into-curried-function&quot;&gt;Transforming &lt;code&gt;UIColor.init()&lt;/code&gt; into curried function&lt;/h3&gt;

&lt;p&gt;Ok, now that we successfully transformed a 2 arguments function into its curried version, let&amp;rsquo;s go back to our goal - transforming &lt;code&gt;UIColor.init(red: green: blue: alpha:)&lt;/code&gt; function that takes 4 arguments (as I mentioned earlier &amp;ndash; same can be applied to any 2+ argument function).&lt;/p&gt;
&lt;div class=&quot;highlight&quot;&gt;&lt;pre&gt;&lt;code class=&quot;language-swift&quot; data-lang=&quot;swift&quot;&gt;&lt;span class=&quot;kd&quot;&gt;func&lt;/span&gt; &lt;span class=&quot;nf&quot;&gt;transformColorInit&lt;/span&gt;&lt;span class=&quot;p&quot;&gt;(&lt;/span&gt;&lt;span class=&quot;nv&quot;&gt;f&lt;/span&gt;&lt;span class=&quot;p&quot;&gt;:&lt;/span&gt; &lt;span class=&quot;kd&quot;&gt;@escaping&lt;/span&gt; &lt;span class=&quot;p&quot;&gt;(&lt;/span&gt;&lt;span class=&quot;kt&quot;&gt;CGFloat&lt;/span&gt;&lt;span class=&quot;p&quot;&gt;,&lt;/span&gt; &lt;span class=&quot;kt&quot;&gt;CGFloat&lt;/span&gt;&lt;span class=&quot;p&quot;&gt;,&lt;/span&gt; &lt;span class=&quot;kt&quot;&gt;CGFloat&lt;/span&gt;&lt;span class=&quot;p&quot;&gt;,&lt;/span&gt; &lt;span class=&quot;kt&quot;&gt;CGFloat&lt;/span&gt;&lt;span class=&quot;p&quot;&gt;)&lt;/span&gt; &lt;span class=&quot;o&quot;&gt;-&amp;gt;&lt;/span&gt; &lt;span class=&quot;kt&quot;&gt;UIColor&lt;/span&gt;&lt;span class=&quot;p&quot;&gt;)&lt;/span&gt; &lt;span class=&quot;o&quot;&gt;-&amp;gt;&lt;/span&gt; &lt;span class=&quot;p&quot;&gt;((&lt;/span&gt;&lt;span class=&quot;kt&quot;&gt;CGFloat&lt;/span&gt;&lt;span class=&quot;p&quot;&gt;)&lt;/span&gt; &lt;span class=&quot;o&quot;&gt;-&amp;gt;&lt;/span&gt; &lt;span class=&quot;p&quot;&gt;(&lt;/span&gt;&lt;span class=&quot;kt&quot;&gt;CGFloat&lt;/span&gt;&lt;span class=&quot;p&quot;&gt;)&lt;/span&gt; &lt;span class=&quot;o&quot;&gt;-&amp;gt;&lt;/span&gt; &lt;span class=&quot;p&quot;&gt;(&lt;/span&gt;&lt;span class=&quot;kt&quot;&gt;CGFloat&lt;/span&gt;&lt;span class=&quot;p&quot;&gt;)&lt;/span&gt; &lt;span class=&quot;o&quot;&gt;-&amp;gt;&lt;/span&gt; &lt;span class=&quot;p&quot;&gt;(&lt;/span&gt;&lt;span class=&quot;kt&quot;&gt;CGFloat&lt;/span&gt;&lt;span class=&quot;p&quot;&gt;)&lt;/span&gt; &lt;span class=&quot;o&quot;&gt;-&amp;gt;&lt;/span&gt; &lt;span class=&quot;kt&quot;&gt;UIColor&lt;/span&gt;&lt;span class=&quot;p&quot;&gt;)&lt;/span&gt; &lt;span class=&quot;p&quot;&gt;{&lt;/span&gt;
    &lt;span class=&quot;k&quot;&gt;return&lt;/span&gt; &lt;span class=&quot;p&quot;&gt;{&lt;/span&gt; &lt;span class=&quot;n&quot;&gt;red&lt;/span&gt; &lt;span class=&quot;k&quot;&gt;in&lt;/span&gt; &lt;span class=&quot;p&quot;&gt;{&lt;/span&gt; &lt;span class=&quot;n&quot;&gt;green&lt;/span&gt; &lt;span class=&quot;k&quot;&gt;in&lt;/span&gt; &lt;span class=&quot;p&quot;&gt;{&lt;/span&gt; &lt;span class=&quot;n&quot;&gt;blue&lt;/span&gt; &lt;span class=&quot;k&quot;&gt;in&lt;/span&gt; &lt;span class=&quot;p&quot;&gt;{&lt;/span&gt; &lt;span class=&quot;n&quot;&gt;alfa&lt;/span&gt; &lt;span class=&quot;k&quot;&gt;in&lt;/span&gt; &lt;span class=&quot;nf&quot;&gt;f&lt;/span&gt;&lt;span class=&quot;p&quot;&gt;(&lt;/span&gt;&lt;span class=&quot;n&quot;&gt;red&lt;/span&gt;&lt;span class=&quot;p&quot;&gt;,&lt;/span&gt; &lt;span class=&quot;n&quot;&gt;green&lt;/span&gt;&lt;span class=&quot;p&quot;&gt;,&lt;/span&gt; &lt;span class=&quot;n&quot;&gt;blue&lt;/span&gt;&lt;span class=&quot;p&quot;&gt;,&lt;/span&gt; &lt;span class=&quot;n&quot;&gt;alfa&lt;/span&gt;&lt;span class=&quot;p&quot;&gt;)&lt;/span&gt; &lt;span class=&quot;p&quot;&gt;}&lt;/span&gt; &lt;span class=&quot;p&quot;&gt;}&lt;/span&gt; &lt;span class=&quot;p&quot;&gt;}&lt;/span&gt; &lt;span class=&quot;p&quot;&gt;}&lt;/span&gt;
&lt;span class=&quot;p&quot;&gt;}&lt;/span&gt;
&lt;/code&gt;&lt;/pre&gt;&lt;/div&gt;
&lt;p&gt;Might look hard to read, but it&amp;rsquo;s quite simple - our &lt;code&gt;transformColorInit&lt;/code&gt; takes as an argument function that matches the signature of &lt;code&gt;UIColor.init(red: green: blue: alpha:)&lt;/code&gt; and it returns a function that takes a float and returns a function, that takes a float and returns a function, that takes a float and returns a function, that takes a float and returns a color.&lt;/p&gt;

&lt;p&gt;General rule is &amp;ndash; you strip away one argument at a time. &lt;br&gt;
If your initial function takes 2 arguments - you will have &lt;code&gt;function returning a function&lt;/code&gt; 2 times. &lt;br&gt;
If it takes 4 arguments (like &lt;code&gt;UIColor.init(...)&lt;/code&gt;), you will have &lt;code&gt;function returning a function&lt;/code&gt; 4 times etc.&lt;br&gt;
Other than the syntax of it looking a bit weird, I think it should be quite easy to understand.&lt;/p&gt;

&lt;p&gt;How do we use our transformer now? As before, we just call it, by passing to it &lt;code&gt;UIColor.init(...)&lt;/code&gt; function.&lt;/p&gt;
&lt;div class=&quot;highlight&quot;&gt;&lt;pre&gt;&lt;code class=&quot;language-swift&quot; data-lang=&quot;swift&quot;&gt;&lt;span class=&quot;k&quot;&gt;let&lt;/span&gt; &lt;span class=&quot;nv&quot;&gt;curriedInit&lt;/span&gt; &lt;span class=&quot;o&quot;&gt;=&lt;/span&gt; &lt;span class=&quot;nf&quot;&gt;transformColorInit&lt;/span&gt;&lt;span class=&quot;p&quot;&gt;(&lt;/span&gt;&lt;span class=&quot;nv&quot;&gt;f&lt;/span&gt;&lt;span class=&quot;p&quot;&gt;:&lt;/span&gt; &lt;span class=&quot;kt&quot;&gt;UIColor&lt;/span&gt;&lt;span class=&quot;o&quot;&gt;.&lt;/span&gt;&lt;span class=&quot;nf&quot;&gt;init&lt;/span&gt;&lt;span class=&quot;p&quot;&gt;(&lt;/span&gt;&lt;span class=&quot;nv&quot;&gt;red&lt;/span&gt;&lt;span class=&quot;p&quot;&gt;:&lt;/span&gt; &lt;span class=&quot;nv&quot;&gt;green&lt;/span&gt;&lt;span class=&quot;p&quot;&gt;:&lt;/span&gt; &lt;span class=&quot;nv&quot;&gt;blue&lt;/span&gt;&lt;span class=&quot;p&quot;&gt;:&lt;/span&gt; &lt;span class=&quot;nv&quot;&gt;alpha&lt;/span&gt;&lt;span class=&quot;p&quot;&gt;:))&lt;/span&gt;
&lt;/code&gt;&lt;/pre&gt;&lt;/div&gt;
&lt;p&gt;&lt;em&gt;(notice that we need to pass full signature of &lt;code&gt;init&lt;/code&gt; function &amp;ndash; it&amp;rsquo;s because &lt;code&gt;UIColor&lt;/code&gt; has more than 1 &lt;code&gt;init&lt;/code&gt; function taking 4 &lt;code&gt;CGFloat&lt;/code&gt; arguments)&lt;/em&gt;&lt;/p&gt;

&lt;p&gt;Now we can e.g. create a function, that will be creating red color with different values of alpha channel (passed as an argument).&lt;/p&gt;
&lt;div class=&quot;highlight&quot;&gt;&lt;pre&gt;&lt;code class=&quot;language-swift&quot; data-lang=&quot;swift&quot;&gt;&lt;span class=&quot;k&quot;&gt;let&lt;/span&gt; &lt;span class=&quot;nv&quot;&gt;createRedWithAlfa&lt;/span&gt; &lt;span class=&quot;o&quot;&gt;=&lt;/span&gt; &lt;span class=&quot;nf&quot;&gt;curriedInit&lt;/span&gt;&lt;span class=&quot;p&quot;&gt;(&lt;/span&gt;&lt;span class=&quot;mi&quot;&gt;1&lt;/span&gt;&lt;span class=&quot;p&quot;&gt;)(&lt;/span&gt;&lt;span class=&quot;mi&quot;&gt;0&lt;/span&gt;&lt;span class=&quot;p&quot;&gt;)(&lt;/span&gt;&lt;span class=&quot;mi&quot;&gt;0&lt;/span&gt;&lt;span class=&quot;p&quot;&gt;)&lt;/span&gt;

&lt;span class=&quot;k&quot;&gt;let&lt;/span&gt; &lt;span class=&quot;nv&quot;&gt;red05&lt;/span&gt; &lt;span class=&quot;o&quot;&gt;=&lt;/span&gt; &lt;span class=&quot;nf&quot;&gt;createRedWithAlfa&lt;/span&gt;&lt;span class=&quot;p&quot;&gt;(&lt;/span&gt;&lt;span class=&quot;mf&quot;&gt;0.5&lt;/span&gt;&lt;span class=&quot;p&quot;&gt;)&lt;/span&gt;
&lt;span class=&quot;k&quot;&gt;let&lt;/span&gt; &lt;span class=&quot;nv&quot;&gt;red02&lt;/span&gt; &lt;span class=&quot;o&quot;&gt;=&lt;/span&gt; &lt;span class=&quot;nf&quot;&gt;createRedWithAlfa&lt;/span&gt;&lt;span class=&quot;p&quot;&gt;(&lt;/span&gt;&lt;span class=&quot;mf&quot;&gt;0.2&lt;/span&gt;&lt;span class=&quot;p&quot;&gt;)&lt;/span&gt;
&lt;span class=&quot;k&quot;&gt;let&lt;/span&gt; &lt;span class=&quot;nv&quot;&gt;red09&lt;/span&gt; &lt;span class=&quot;o&quot;&gt;=&lt;/span&gt; &lt;span class=&quot;nf&quot;&gt;createRedWithAlfa&lt;/span&gt;&lt;span class=&quot;p&quot;&gt;(&lt;/span&gt;&lt;span class=&quot;mf&quot;&gt;0.9&lt;/span&gt;&lt;span class=&quot;p&quot;&gt;)&lt;/span&gt;
&lt;/code&gt;&lt;/pre&gt;&lt;/div&gt;
&lt;p&gt;Of course, you&amp;rsquo;re not limited to just last argument, you could also make a function taking 2 or 3 arguments if you needed to:&lt;/p&gt;
&lt;div class=&quot;highlight&quot;&gt;&lt;pre&gt;&lt;code class=&quot;language-swift&quot; data-lang=&quot;swift&quot;&gt;&lt;span class=&quot;k&quot;&gt;let&lt;/span&gt; &lt;span class=&quot;nv&quot;&gt;createBlueColorWithAlpha&lt;/span&gt; &lt;span class=&quot;o&quot;&gt;=&lt;/span&gt; &lt;span class=&quot;nf&quot;&gt;curriedInit&lt;/span&gt;&lt;span class=&quot;p&quot;&gt;(&lt;/span&gt;&lt;span class=&quot;mi&quot;&gt;0&lt;/span&gt;&lt;span class=&quot;p&quot;&gt;)(&lt;/span&gt;&lt;span class=&quot;mi&quot;&gt;0&lt;/span&gt;&lt;span class=&quot;p&quot;&gt;)&lt;/span&gt;

&lt;span class=&quot;k&quot;&gt;let&lt;/span&gt; &lt;span class=&quot;nv&quot;&gt;semiTransparentBlue&lt;/span&gt; &lt;span class=&quot;o&quot;&gt;=&lt;/span&gt; &lt;span class=&quot;nf&quot;&gt;createBlueColorWithAlpha&lt;/span&gt;&lt;span class=&quot;p&quot;&gt;(&lt;/span&gt;&lt;span class=&quot;mi&quot;&gt;1&lt;/span&gt;&lt;span class=&quot;p&quot;&gt;)(&lt;/span&gt;&lt;span class=&quot;mf&quot;&gt;0.5&lt;/span&gt;&lt;span class=&quot;p&quot;&gt;)&lt;/span&gt;
&lt;span class=&quot;k&quot;&gt;let&lt;/span&gt; &lt;span class=&quot;nv&quot;&gt;solidBlue&lt;/span&gt; &lt;span class=&quot;o&quot;&gt;=&lt;/span&gt; &lt;span class=&quot;nf&quot;&gt;createBlueColorWithAlpha&lt;/span&gt;&lt;span class=&quot;p&quot;&gt;(&lt;/span&gt;&lt;span class=&quot;mi&quot;&gt;1&lt;/span&gt;&lt;span class=&quot;p&quot;&gt;)(&lt;/span&gt;&lt;span class=&quot;mi&quot;&gt;1&lt;/span&gt;&lt;span class=&quot;p&quot;&gt;)&lt;/span&gt;
&lt;/code&gt;&lt;/pre&gt;&lt;/div&gt;
&lt;h3 id=&quot;generic-tranforming-function&quot;&gt;Generic tranforming function&lt;/h3&gt;

&lt;p&gt;Do we need to write a different transforming function for every function that we want to transform? Fortunately, the answer is &lt;code&gt;NO&lt;/code&gt;.&lt;/p&gt;

&lt;p&gt;We can use the power of Swift&amp;rsquo;s generics and write a generic function, that will take as an argument function with non-specified argument types (can be Int, Float, String, Class type etc) and return its curried version.&lt;/p&gt;

&lt;p&gt;For 4 argument function (like &lt;code&gt;UIColor.init(...)&lt;/code&gt;) it could look like this:&lt;/p&gt;
&lt;div class=&quot;highlight&quot;&gt;&lt;pre&gt;&lt;code class=&quot;language-swift&quot; data-lang=&quot;swift&quot;&gt;&lt;span class=&quot;kd&quot;&gt;public&lt;/span&gt; &lt;span class=&quot;kd&quot;&gt;func&lt;/span&gt; &lt;span class=&quot;n&quot;&gt;curry&lt;/span&gt;&lt;span class=&quot;o&quot;&gt;&amp;lt;&lt;/span&gt;&lt;span class=&quot;kt&quot;&gt;A&lt;/span&gt;&lt;span class=&quot;p&quot;&gt;,&lt;/span&gt; &lt;span class=&quot;kt&quot;&gt;B&lt;/span&gt;&lt;span class=&quot;p&quot;&gt;,&lt;/span&gt; &lt;span class=&quot;kt&quot;&gt;C&lt;/span&gt;&lt;span class=&quot;p&quot;&gt;,&lt;/span&gt; &lt;span class=&quot;kt&quot;&gt;D&lt;/span&gt;&lt;span class=&quot;p&quot;&gt;,&lt;/span&gt; &lt;span class=&quot;kt&quot;&gt;E&lt;/span&gt;&lt;span class=&quot;o&quot;&gt;&amp;gt;&lt;/span&gt;&lt;span class=&quot;p&quot;&gt;(&lt;/span&gt;&lt;span class=&quot;n&quot;&gt;_&lt;/span&gt; &lt;span class=&quot;nv&quot;&gt;function&lt;/span&gt;&lt;span class=&quot;p&quot;&gt;:&lt;/span&gt; &lt;span class=&quot;kd&quot;&gt;@escaping&lt;/span&gt; &lt;span class=&quot;p&quot;&gt;(&lt;/span&gt;&lt;span class=&quot;kt&quot;&gt;A&lt;/span&gt;&lt;span class=&quot;p&quot;&gt;,&lt;/span&gt; &lt;span class=&quot;kt&quot;&gt;B&lt;/span&gt;&lt;span class=&quot;p&quot;&gt;,&lt;/span&gt; &lt;span class=&quot;kt&quot;&gt;C&lt;/span&gt;&lt;span class=&quot;p&quot;&gt;,&lt;/span&gt; &lt;span class=&quot;kt&quot;&gt;D&lt;/span&gt;&lt;span class=&quot;p&quot;&gt;)&lt;/span&gt; &lt;span class=&quot;o&quot;&gt;-&amp;gt;&lt;/span&gt; &lt;span class=&quot;kt&quot;&gt;E&lt;/span&gt;&lt;span class=&quot;p&quot;&gt;)&lt;/span&gt; &lt;span class=&quot;o&quot;&gt;-&amp;gt;&lt;/span&gt; &lt;span class=&quot;p&quot;&gt;(&lt;/span&gt;&lt;span class=&quot;kt&quot;&gt;A&lt;/span&gt;&lt;span class=&quot;p&quot;&gt;)&lt;/span&gt; &lt;span class=&quot;o&quot;&gt;-&amp;gt;&lt;/span&gt; &lt;span class=&quot;p&quot;&gt;(&lt;/span&gt;&lt;span class=&quot;kt&quot;&gt;B&lt;/span&gt;&lt;span class=&quot;p&quot;&gt;)&lt;/span&gt; &lt;span class=&quot;o&quot;&gt;-&amp;gt;&lt;/span&gt; &lt;span class=&quot;p&quot;&gt;(&lt;/span&gt;&lt;span class=&quot;kt&quot;&gt;C&lt;/span&gt;&lt;span class=&quot;p&quot;&gt;)&lt;/span&gt; &lt;span class=&quot;o&quot;&gt;-&amp;gt;&lt;/span&gt; &lt;span class=&quot;p&quot;&gt;(&lt;/span&gt;&lt;span class=&quot;kt&quot;&gt;D&lt;/span&gt;&lt;span class=&quot;p&quot;&gt;)&lt;/span&gt; &lt;span class=&quot;o&quot;&gt;-&amp;gt;&lt;/span&gt; &lt;span class=&quot;kt&quot;&gt;E&lt;/span&gt; &lt;span class=&quot;p&quot;&gt;{&lt;/span&gt;
    &lt;span class=&quot;k&quot;&gt;return&lt;/span&gt; &lt;span class=&quot;p&quot;&gt;{&lt;/span&gt; &lt;span class=&quot;p&quot;&gt;(&lt;/span&gt;&lt;span class=&quot;nv&quot;&gt;a&lt;/span&gt;&lt;span class=&quot;p&quot;&gt;:&lt;/span&gt; &lt;span class=&quot;kt&quot;&gt;A&lt;/span&gt;&lt;span class=&quot;p&quot;&gt;)&lt;/span&gt; &lt;span class=&quot;o&quot;&gt;-&amp;gt;&lt;/span&gt; &lt;span class=&quot;p&quot;&gt;(&lt;/span&gt;&lt;span class=&quot;kt&quot;&gt;B&lt;/span&gt;&lt;span class=&quot;p&quot;&gt;)&lt;/span&gt; &lt;span class=&quot;o&quot;&gt;-&amp;gt;&lt;/span&gt; &lt;span class=&quot;p&quot;&gt;(&lt;/span&gt;&lt;span class=&quot;kt&quot;&gt;C&lt;/span&gt;&lt;span class=&quot;p&quot;&gt;)&lt;/span&gt; &lt;span class=&quot;o&quot;&gt;-&amp;gt;&lt;/span&gt; &lt;span class=&quot;p&quot;&gt;(&lt;/span&gt;&lt;span class=&quot;kt&quot;&gt;D&lt;/span&gt;&lt;span class=&quot;p&quot;&gt;)&lt;/span&gt; &lt;span class=&quot;o&quot;&gt;-&amp;gt;&lt;/span&gt; &lt;span class=&quot;kt&quot;&gt;E&lt;/span&gt; &lt;span class=&quot;k&quot;&gt;in&lt;/span&gt; &lt;span class=&quot;p&quot;&gt;{&lt;/span&gt; &lt;span class=&quot;p&quot;&gt;(&lt;/span&gt;&lt;span class=&quot;nv&quot;&gt;b&lt;/span&gt;&lt;span class=&quot;p&quot;&gt;:&lt;/span&gt; &lt;span class=&quot;kt&quot;&gt;B&lt;/span&gt;&lt;span class=&quot;p&quot;&gt;)&lt;/span&gt; &lt;span class=&quot;o&quot;&gt;-&amp;gt;&lt;/span&gt; &lt;span class=&quot;p&quot;&gt;(&lt;/span&gt;&lt;span class=&quot;kt&quot;&gt;C&lt;/span&gt;&lt;span class=&quot;p&quot;&gt;)&lt;/span&gt; &lt;span class=&quot;o&quot;&gt;-&amp;gt;&lt;/span&gt; &lt;span class=&quot;p&quot;&gt;(&lt;/span&gt;&lt;span class=&quot;kt&quot;&gt;D&lt;/span&gt;&lt;span class=&quot;p&quot;&gt;)&lt;/span&gt; &lt;span class=&quot;o&quot;&gt;-&amp;gt;&lt;/span&gt; &lt;span class=&quot;kt&quot;&gt;E&lt;/span&gt; &lt;span class=&quot;k&quot;&gt;in&lt;/span&gt; &lt;span class=&quot;p&quot;&gt;{&lt;/span&gt; &lt;span class=&quot;p&quot;&gt;(&lt;/span&gt;&lt;span class=&quot;nv&quot;&gt;c&lt;/span&gt;&lt;span class=&quot;p&quot;&gt;:&lt;/span&gt; &lt;span class=&quot;kt&quot;&gt;C&lt;/span&gt;&lt;span class=&quot;p&quot;&gt;)&lt;/span&gt; &lt;span class=&quot;o&quot;&gt;-&amp;gt;&lt;/span&gt; &lt;span class=&quot;p&quot;&gt;(&lt;/span&gt;&lt;span class=&quot;kt&quot;&gt;D&lt;/span&gt;&lt;span class=&quot;p&quot;&gt;)&lt;/span&gt; &lt;span class=&quot;o&quot;&gt;-&amp;gt;&lt;/span&gt; &lt;span class=&quot;kt&quot;&gt;E&lt;/span&gt; &lt;span class=&quot;k&quot;&gt;in&lt;/span&gt; &lt;span class=&quot;p&quot;&gt;{&lt;/span&gt; &lt;span class=&quot;p&quot;&gt;(&lt;/span&gt;&lt;span class=&quot;nv&quot;&gt;d&lt;/span&gt;&lt;span class=&quot;p&quot;&gt;:&lt;/span&gt; &lt;span class=&quot;kt&quot;&gt;D&lt;/span&gt;&lt;span class=&quot;p&quot;&gt;)&lt;/span&gt; &lt;span class=&quot;o&quot;&gt;-&amp;gt;&lt;/span&gt; &lt;span class=&quot;kt&quot;&gt;E&lt;/span&gt; &lt;span class=&quot;k&quot;&gt;in&lt;/span&gt; &lt;span class=&quot;nf&quot;&gt;function&lt;/span&gt;&lt;span class=&quot;p&quot;&gt;(&lt;/span&gt;&lt;span class=&quot;n&quot;&gt;a&lt;/span&gt;&lt;span class=&quot;p&quot;&gt;,&lt;/span&gt; &lt;span class=&quot;n&quot;&gt;b&lt;/span&gt;&lt;span class=&quot;p&quot;&gt;,&lt;/span&gt; &lt;span class=&quot;n&quot;&gt;c&lt;/span&gt;&lt;span class=&quot;p&quot;&gt;,&lt;/span&gt; &lt;span class=&quot;n&quot;&gt;d&lt;/span&gt;&lt;span class=&quot;p&quot;&gt;)&lt;/span&gt; &lt;span class=&quot;p&quot;&gt;}&lt;/span&gt; &lt;span class=&quot;p&quot;&gt;}&lt;/span&gt; &lt;span class=&quot;p&quot;&gt;}&lt;/span&gt; &lt;span class=&quot;p&quot;&gt;}&lt;/span&gt;
&lt;span class=&quot;p&quot;&gt;}&lt;/span&gt;
&lt;/code&gt;&lt;/pre&gt;&lt;/div&gt;
&lt;p&gt;It is a generic function with 5 different placeholder types &amp;ndash; 4 of them for arguments of passed function and 1 for its return type. Of course, nothing stops us from passing a function that has all 4 arguments of the same type.&lt;/p&gt;
&lt;div class=&quot;highlight&quot;&gt;&lt;pre&gt;&lt;code class=&quot;language-swift&quot; data-lang=&quot;swift&quot;&gt;&lt;span class=&quot;k&quot;&gt;let&lt;/span&gt; &lt;span class=&quot;nv&quot;&gt;createRedWithAlfaV2&lt;/span&gt; &lt;span class=&quot;o&quot;&gt;=&lt;/span&gt; &lt;span class=&quot;nf&quot;&gt;curry&lt;/span&gt;&lt;span class=&quot;p&quot;&gt;(&lt;/span&gt;&lt;span class=&quot;kt&quot;&gt;UIColor&lt;/span&gt;&lt;span class=&quot;o&quot;&gt;.&lt;/span&gt;&lt;span class=&quot;nf&quot;&gt;init&lt;/span&gt;&lt;span class=&quot;p&quot;&gt;(&lt;/span&gt;&lt;span class=&quot;nv&quot;&gt;red&lt;/span&gt;&lt;span class=&quot;p&quot;&gt;:&lt;/span&gt; &lt;span class=&quot;nv&quot;&gt;green&lt;/span&gt;&lt;span class=&quot;p&quot;&gt;:&lt;/span&gt; &lt;span class=&quot;nv&quot;&gt;blue&lt;/span&gt;&lt;span class=&quot;p&quot;&gt;:&lt;/span&gt; &lt;span class=&quot;nv&quot;&gt;alpha&lt;/span&gt;&lt;span class=&quot;p&quot;&gt;:))(&lt;/span&gt;&lt;span class=&quot;mi&quot;&gt;1&lt;/span&gt;&lt;span class=&quot;p&quot;&gt;)(&lt;/span&gt;&lt;span class=&quot;mi&quot;&gt;0&lt;/span&gt;&lt;span class=&quot;p&quot;&gt;)(&lt;/span&gt;&lt;span class=&quot;mi&quot;&gt;0&lt;/span&gt;&lt;span class=&quot;p&quot;&gt;)&lt;/span&gt;

&lt;span class=&quot;k&quot;&gt;let&lt;/span&gt; &lt;span class=&quot;nv&quot;&gt;red01&lt;/span&gt; &lt;span class=&quot;o&quot;&gt;=&lt;/span&gt; &lt;span class=&quot;nf&quot;&gt;createRedWithAlfaV2&lt;/span&gt;&lt;span class=&quot;p&quot;&gt;(&lt;/span&gt;&lt;span class=&quot;mf&quot;&gt;0.1&lt;/span&gt;&lt;span class=&quot;p&quot;&gt;)&lt;/span&gt;
&lt;/code&gt;&lt;/pre&gt;&lt;/div&gt;
&lt;p&gt;Code for &lt;code&gt;curry&lt;/code&gt; function was written by guys from &lt;a href=&quot;https://github.com/thoughtbot/Curry/blob/master/Source/Curry.swift&quot;&gt;thoughbot&lt;/a&gt; &amp;ndash; feel free to take a look and see an example for function transforming a function taking 20 arguments :)&lt;/p&gt;

&lt;hr&gt;

&lt;p&gt;That&amp;rsquo;s it for today. You should know what function currying is, how to use it and how to transform any 2+ argument function into its curried version. If you have any questions &amp;ndash; let me know in comments!&lt;/p&gt;

&lt;hr&gt;

&lt;p&gt;Sources (I recommend you to read first 3 positions, they did help me to understand better what function currying is!):&lt;/p&gt;

&lt;ul&gt;
&lt;li&gt;&lt;a href=&quot;https://robots.thoughtbot.com/introduction-to-function-currying-in-swift&quot;&gt;thoughtbot Blog&lt;/a&gt;&lt;/li&gt;
&lt;li&gt;&lt;a href=&quot;https://yeti.co/blog/using-curried-functions-in-swift/&quot;&gt;Yeti.co Blog&lt;/a&gt;&lt;/li&gt;
&lt;li&gt;&lt;a href=&quot;https://otters.io/a-little-less-spice-in-swift-3&quot;&gt;Otters.io Blog&lt;/a&gt;&lt;/li&gt;
&lt;li&gt;&lt;a href=&quot;https://github.com/apple/swift-evolution/blob/master/proposals/0002-remove-currying.md&quot;&gt;Proposal for removing currying &lt;code&gt;func&lt;/code&gt; declaration syntax in Swift 3&lt;/a&gt;&lt;/li&gt;
&lt;li&gt;&lt;a href=&quot;https://developer.apple.com/library/content/documentation/Swift/Conceptual/Swift_Programming_Language/Closures.html&quot;&gt;Apple Closure docs&lt;/a&gt;&lt;/li&gt;
&lt;/ul&gt;
</description>
        <pubDate>Fri, 10 Feb 2017 11:00:00 -0500</pubDate>
        <link>http://iosdev.nyc/blog/function-currying-swift/</link>
        <guid isPermaLink="true">http://iosdev.nyc/blog/function-currying-swift/</guid>
      </item>
    
      <item>
        <title>Pyramid of Doom Updated (Swift 3)</title>
        <description>&lt;p&gt;Since last posts about using &lt;code&gt;let&lt;/code&gt; and &lt;code&gt;guard&lt;/code&gt;, Swift 3 came out and changed a few things here and there. Let&amp;rsquo;s see what&amp;rsquo;s new! &lt;/p&gt;

&lt;p&gt;Let&amp;rsquo;s start from the beginning - the basics are still the same. So still, please don&amp;rsquo;t do:&lt;/p&gt;
&lt;div class=&quot;highlight&quot;&gt;&lt;pre&gt;&lt;code class=&quot;language-&quot; data-lang=&quot;&quot;&gt;if let x = x {
    if let y = y {
        if let z = z {
            print(&quot;x = \(x), y = \(y), z = \(z)&quot;)
            x * y * z * 3
        }
    }
}
&lt;/code&gt;&lt;/pre&gt;&lt;/div&gt;
&lt;p&gt;or&lt;/p&gt;
&lt;div class=&quot;highlight&quot;&gt;&lt;pre&gt;&lt;code class=&quot;language-&quot; data-lang=&quot;&quot;&gt;func objcStyle(foo: Int?, bar: Int?) {
    if (foo == nil || bar == nil) {
        return
    }
    let a = foo!
    let b = bar!
    a.advanced(by: b)
    // or force unwrap both directly with
    // a!.advanceBy(by: b)
}
&lt;/code&gt;&lt;/pre&gt;&lt;/div&gt;
&lt;p&gt;and instead do these two:&lt;/p&gt;
&lt;div class=&quot;highlight&quot;&gt;&lt;pre&gt;&lt;code class=&quot;language-&quot; data-lang=&quot;&quot;&gt;if let x = x, let y = y, let z = z {
    print(&quot;x = \(x), y = \(y), z = \(z)&quot;)
    x * y * z * 3
}
&lt;/code&gt;&lt;/pre&gt;&lt;/div&gt;
&lt;p&gt;and&lt;/p&gt;
&lt;div class=&quot;highlight&quot;&gt;&lt;pre&gt;&lt;code class=&quot;language-&quot; data-lang=&quot;&quot;&gt;func swiftGuardStyle(foo: Int?, bar: Int?) {
    guard let a = foo, let b = bar else {
        return
    }
    a.advanced(by: b)
}
&lt;/code&gt;&lt;/pre&gt;&lt;/div&gt;
&lt;p&gt;In short - use Swift like it was meant to be, not like you would be writing Obj-C, jus using Swift syntax.&lt;/p&gt;

&lt;p&gt;One important change is using &lt;code&gt;where&lt;/code&gt; clause. For full summary of changes, you can visit &lt;a href=&quot;https://github.com/apple/swift-evolution/blob/master/proposals/0099-conditionclauses.md&quot;&gt;Swift Evolution&lt;/a&gt;.&lt;/p&gt;

&lt;p&gt;In short - now, this change makes each clause in &lt;code&gt;if&lt;/code&gt; statement separate from each other and limits clauses to a single item. To make it easier to understand, take a look at Swift 2 and 3 examples below:&lt;/p&gt;
&lt;div class=&quot;highlight&quot;&gt;&lt;pre&gt;&lt;code class=&quot;language-&quot; data-lang=&quot;&quot;&gt;// SWIFT 2
func swiftGuardStyleWhere(book: Book?, author: Author?, rating: Int) {
    guard rating &amp;gt; 4, let book = book, author = author where author == &quot;Bob&quot; else {
        return
    }
    // will only execute if book and author are non nil
    // and when author&#39;s name is &quot;Bob&quot;
    // and when rating is &amp;gt; 4
    doSomething()
}
&lt;/code&gt;&lt;/pre&gt;&lt;/div&gt;&lt;div class=&quot;highlight&quot;&gt;&lt;pre&gt;&lt;code class=&quot;language-&quot; data-lang=&quot;&quot;&gt;func swiftGuardStyleWhere(book: Book?, author: Author?, rating: Int) {
    guard rating &amp;gt; 4, let book = book, let author = author, author == &quot;Bob&quot; else {
        return
    }
    // will only execute if book and author are non nil
    // and when author&#39;s name is &quot;Bob&quot;
    // and when rating is &amp;gt; 4
}
&lt;/code&gt;&lt;/pre&gt;&lt;/div&gt;
&lt;p&gt;What&amp;rsquo;s different?&lt;/p&gt;

&lt;ul&gt;
&lt;li&gt;Because each clause is now separated by &lt;code&gt;,&lt;/code&gt;, you need to type &lt;code&gt;let&lt;/code&gt; in each clause &amp;ndash; before all confitional binding statements (it doesn&amp;rsquo;t propagate)&lt;/li&gt;
&lt;li&gt;&lt;code&gt;where&lt;/code&gt; keyword is removed and replaced by &lt;code&gt;,&lt;/code&gt; &amp;ndash; each sub-clause of the &lt;code&gt;if&lt;/code&gt; statement is now an independent boolean test&lt;/li&gt;
&lt;/ul&gt;

&lt;p&gt;That&amp;rsquo;s really it &amp;ndash; when it comes to topics covered by previous two blog posts, nothing else changed. Make sure to get rid of &lt;code&gt;where&lt;/code&gt; clause from your &lt;code&gt;if&lt;/code&gt; statements and repeat &lt;code&gt;let&lt;/code&gt; for every sub-clause and you will be fine!&lt;/p&gt;
</description>
        <pubDate>Tue, 07 Feb 2017 01:00:00 -0500</pubDate>
        <link>http://iosdev.nyc/blog/let-guard-pyramid-of-doom-swift-3/</link>
        <guid isPermaLink="true">http://iosdev.nyc/blog/let-guard-pyramid-of-doom-swift-3/</guid>
      </item>
    
      <item>
        <title>Dealing with Swift&#39;s Pyramid of Doom</title>
        <description>&lt;p&gt;&lt;strong&gt;Update, 07 Feb 2017&lt;/strong&gt;&lt;br&gt;
As of Swift 3, some of the code below may not work properly anymore. To see what changed, read &lt;a href=&quot;/blog/let-guard-pyramid-of-doom-swift-3/&quot;&gt;Pyramid of Doom Updated (Swift 3)&lt;/a&gt;.&lt;/p&gt;

&lt;hr&gt;

&lt;p&gt;&lt;strong&gt;Original Post&lt;/strong&gt;&lt;/p&gt;

&lt;p&gt;Today we continue the topic of avoiding Swift’s &lt;a href=&quot;http://blog.scottlogic.com/2014/12/08/swift-optional-pyramids-of-doom.html&quot;&gt;&lt;em&gt;Pyramid of Doom&lt;/em&gt;&lt;/a&gt; that we started in &lt;a href=&quot;/blog/let-guard/&quot;&gt;previous post&lt;/a&gt;, on &lt;code&gt;guard&lt;/code&gt; statement. &lt;br&gt;
This time, we cover a feature from Swift 1.2 – it’s not a new thing, but still very handy and useful to have in your arsenal.&lt;/p&gt;

&lt;p&gt;Every now and then I see older code that does something like this:&lt;/p&gt;
&lt;div class=&quot;highlight&quot;&gt;&lt;pre&gt;&lt;code class=&quot;language-swift&quot; data-lang=&quot;swift&quot;&gt;&lt;span class=&quot;kd&quot;&gt;func&lt;/span&gt; &lt;span class=&quot;nf&quot;&gt;pyramidOfDoom&lt;/span&gt;&lt;span class=&quot;p&quot;&gt;(&lt;/span&gt;&lt;span class=&quot;nv&quot;&gt;x&lt;/span&gt;&lt;span class=&quot;p&quot;&gt;:&lt;/span&gt; &lt;span class=&quot;kt&quot;&gt;Int&lt;/span&gt;&lt;span class=&quot;p&quot;&gt;?,&lt;/span&gt; &lt;span class=&quot;nv&quot;&gt;y&lt;/span&gt;&lt;span class=&quot;p&quot;&gt;:&lt;/span&gt; &lt;span class=&quot;kt&quot;&gt;Int&lt;/span&gt;&lt;span class=&quot;p&quot;&gt;?,&lt;/span&gt; &lt;span class=&quot;nv&quot;&gt;z&lt;/span&gt;&lt;span class=&quot;p&quot;&gt;:&lt;/span&gt; &lt;span class=&quot;kt&quot;&gt;Int&lt;/span&gt;&lt;span class=&quot;p&quot;&gt;?)&lt;/span&gt; &lt;span class=&quot;p&quot;&gt;{&lt;/span&gt;
    &lt;span class=&quot;k&quot;&gt;if&lt;/span&gt; &lt;span class=&quot;k&quot;&gt;let&lt;/span&gt; &lt;span class=&quot;nv&quot;&gt;x&lt;/span&gt; &lt;span class=&quot;o&quot;&gt;=&lt;/span&gt; &lt;span class=&quot;n&quot;&gt;x&lt;/span&gt; &lt;span class=&quot;p&quot;&gt;{&lt;/span&gt;
        &lt;span class=&quot;k&quot;&gt;if&lt;/span&gt; &lt;span class=&quot;k&quot;&gt;let&lt;/span&gt; &lt;span class=&quot;nv&quot;&gt;y&lt;/span&gt; &lt;span class=&quot;o&quot;&gt;=&lt;/span&gt; &lt;span class=&quot;n&quot;&gt;y&lt;/span&gt; &lt;span class=&quot;p&quot;&gt;{&lt;/span&gt;
            &lt;span class=&quot;k&quot;&gt;if&lt;/span&gt; &lt;span class=&quot;k&quot;&gt;let&lt;/span&gt; &lt;span class=&quot;nv&quot;&gt;z&lt;/span&gt; &lt;span class=&quot;o&quot;&gt;=&lt;/span&gt; &lt;span class=&quot;n&quot;&gt;z&lt;/span&gt; &lt;span class=&quot;p&quot;&gt;{&lt;/span&gt;
                &lt;span class=&quot;c1&quot;&gt;//do something with x, y and z&lt;/span&gt;
                &lt;span class=&quot;nf&quot;&gt;print&lt;/span&gt;&lt;span class=&quot;p&quot;&gt;(&lt;/span&gt;&lt;span class=&quot;s&quot;&gt;&quot;&lt;/span&gt;&lt;span class=&quot;se&quot;&gt;\(&lt;/span&gt;&lt;span class=&quot;n&quot;&gt;x&lt;/span&gt;&lt;span class=&quot;p&quot;&gt;,&lt;/span&gt; &lt;span class=&quot;n&quot;&gt;y&lt;/span&gt;&lt;span class=&quot;p&quot;&gt;,&lt;/span&gt; &lt;span class=&quot;n&quot;&gt;z&lt;/span&gt;&lt;span class=&quot;se&quot;&gt;)&lt;/span&gt;&lt;span class=&quot;s&quot;&gt;&quot;&lt;/span&gt;&lt;span class=&quot;p&quot;&gt;)&lt;/span&gt;
            &lt;span class=&quot;p&quot;&gt;}&lt;/span&gt;
        &lt;span class=&quot;p&quot;&gt;}&lt;/span&gt;
    &lt;span class=&quot;p&quot;&gt;}&lt;/span&gt;
&lt;span class=&quot;p&quot;&gt;}&lt;/span&gt;
&lt;/code&gt;&lt;/pre&gt;&lt;/div&gt;
&lt;p&gt;It works and was necessary in Swift 1.0 (unless you added your own workaround for it).&lt;/p&gt;

&lt;p&gt;In Swift 1.2, &lt;code&gt;if let&lt;/code&gt; allows unwrapping multiple optionals, which lets us rewrite previous example into&lt;/p&gt;
&lt;div class=&quot;highlight&quot;&gt;&lt;pre&gt;&lt;code class=&quot;language-swift&quot; data-lang=&quot;swift&quot;&gt;&lt;span class=&quot;kd&quot;&gt;func&lt;/span&gt; &lt;span class=&quot;nf&quot;&gt;noPyramid&lt;/span&gt;&lt;span class=&quot;p&quot;&gt;(&lt;/span&gt;&lt;span class=&quot;nv&quot;&gt;x&lt;/span&gt;&lt;span class=&quot;p&quot;&gt;:&lt;/span&gt; &lt;span class=&quot;kt&quot;&gt;Int&lt;/span&gt;&lt;span class=&quot;p&quot;&gt;?,&lt;/span&gt; &lt;span class=&quot;nv&quot;&gt;y&lt;/span&gt;&lt;span class=&quot;p&quot;&gt;:&lt;/span&gt; &lt;span class=&quot;kt&quot;&gt;Int&lt;/span&gt;&lt;span class=&quot;p&quot;&gt;?,&lt;/span&gt; &lt;span class=&quot;nv&quot;&gt;z&lt;/span&gt;&lt;span class=&quot;p&quot;&gt;:&lt;/span&gt; &lt;span class=&quot;kt&quot;&gt;Int&lt;/span&gt;&lt;span class=&quot;p&quot;&gt;?)&lt;/span&gt; &lt;span class=&quot;p&quot;&gt;{&lt;/span&gt;
    &lt;span class=&quot;k&quot;&gt;if&lt;/span&gt; &lt;span class=&quot;k&quot;&gt;let&lt;/span&gt; &lt;span class=&quot;nv&quot;&gt;x&lt;/span&gt; &lt;span class=&quot;o&quot;&gt;=&lt;/span&gt; &lt;span class=&quot;n&quot;&gt;x&lt;/span&gt;&lt;span class=&quot;p&quot;&gt;,&lt;/span&gt; &lt;span class=&quot;n&quot;&gt;y&lt;/span&gt; &lt;span class=&quot;o&quot;&gt;=&lt;/span&gt; &lt;span class=&quot;n&quot;&gt;y&lt;/span&gt;&lt;span class=&quot;p&quot;&gt;,&lt;/span&gt; &lt;span class=&quot;n&quot;&gt;z&lt;/span&gt; &lt;span class=&quot;o&quot;&gt;=&lt;/span&gt; &lt;span class=&quot;n&quot;&gt;z&lt;/span&gt; &lt;span class=&quot;p&quot;&gt;{&lt;/span&gt;
        &lt;span class=&quot;c1&quot;&gt;//do something with x, y and z&lt;/span&gt;
        &lt;span class=&quot;nf&quot;&gt;print&lt;/span&gt;&lt;span class=&quot;p&quot;&gt;(&lt;/span&gt;&lt;span class=&quot;s&quot;&gt;&quot;&lt;/span&gt;&lt;span class=&quot;se&quot;&gt;\(&lt;/span&gt;&lt;span class=&quot;n&quot;&gt;x&lt;/span&gt;&lt;span class=&quot;p&quot;&gt;,&lt;/span&gt; &lt;span class=&quot;n&quot;&gt;y&lt;/span&gt;&lt;span class=&quot;p&quot;&gt;,&lt;/span&gt; &lt;span class=&quot;n&quot;&gt;z&lt;/span&gt;&lt;span class=&quot;se&quot;&gt;)&lt;/span&gt;&lt;span class=&quot;s&quot;&gt;&quot;&lt;/span&gt;&lt;span class=&quot;p&quot;&gt;)&lt;/span&gt;
    &lt;span class=&quot;p&quot;&gt;}&lt;/span&gt;
&lt;span class=&quot;p&quot;&gt;}&lt;/span&gt;
&lt;/code&gt;&lt;/pre&gt;&lt;/div&gt;
&lt;p&gt;So much better!&lt;/p&gt;

&lt;p&gt;What’s also useful and helpful for keeping your code clean, is the ability to add &lt;code&gt;where&lt;/code&gt; clause to your optional binding. &lt;br&gt;
It lets you check not only if optionals hold any value, but also if that value meets certain condition.&lt;/p&gt;

&lt;p&gt;Let’s take a look at code we would write normally, using &lt;code&gt;if&lt;/code&gt; statement&lt;/p&gt;
&lt;div class=&quot;highlight&quot;&gt;&lt;pre&gt;&lt;code class=&quot;language-swift&quot; data-lang=&quot;swift&quot;&gt;&lt;span class=&quot;kd&quot;&gt;func&lt;/span&gt; &lt;span class=&quot;nf&quot;&gt;ifStatement&lt;/span&gt;&lt;span class=&quot;p&quot;&gt;(&lt;/span&gt;&lt;span class=&quot;nv&quot;&gt;x&lt;/span&gt;&lt;span class=&quot;p&quot;&gt;:&lt;/span&gt; &lt;span class=&quot;kt&quot;&gt;Int&lt;/span&gt;&lt;span class=&quot;p&quot;&gt;?,&lt;/span&gt; &lt;span class=&quot;nv&quot;&gt;y&lt;/span&gt;&lt;span class=&quot;p&quot;&gt;:&lt;/span&gt; &lt;span class=&quot;kt&quot;&gt;Int&lt;/span&gt;&lt;span class=&quot;p&quot;&gt;?,&lt;/span&gt; &lt;span class=&quot;nv&quot;&gt;z&lt;/span&gt;&lt;span class=&quot;p&quot;&gt;:&lt;/span&gt; &lt;span class=&quot;kt&quot;&gt;Int&lt;/span&gt;&lt;span class=&quot;p&quot;&gt;?)&lt;/span&gt; &lt;span class=&quot;p&quot;&gt;{&lt;/span&gt;
    &lt;span class=&quot;k&quot;&gt;if&lt;/span&gt; &lt;span class=&quot;k&quot;&gt;let&lt;/span&gt; &lt;span class=&quot;nv&quot;&gt;x&lt;/span&gt; &lt;span class=&quot;o&quot;&gt;=&lt;/span&gt; &lt;span class=&quot;n&quot;&gt;x&lt;/span&gt;&lt;span class=&quot;p&quot;&gt;,&lt;/span&gt; &lt;span class=&quot;n&quot;&gt;y&lt;/span&gt; &lt;span class=&quot;o&quot;&gt;=&lt;/span&gt; &lt;span class=&quot;n&quot;&gt;y&lt;/span&gt;&lt;span class=&quot;p&quot;&gt;,&lt;/span&gt; &lt;span class=&quot;n&quot;&gt;z&lt;/span&gt; &lt;span class=&quot;o&quot;&gt;=&lt;/span&gt; &lt;span class=&quot;n&quot;&gt;z&lt;/span&gt; &lt;span class=&quot;p&quot;&gt;{&lt;/span&gt;
        &lt;span class=&quot;k&quot;&gt;if&lt;/span&gt; &lt;span class=&quot;p&quot;&gt;(&lt;/span&gt;&lt;span class=&quot;n&quot;&gt;z&lt;/span&gt; &lt;span class=&quot;o&quot;&gt;&amp;lt;&lt;/span&gt; &lt;span class=&quot;mi&quot;&gt;4&lt;/span&gt;&lt;span class=&quot;p&quot;&gt;)&lt;/span&gt; &lt;span class=&quot;p&quot;&gt;{&lt;/span&gt;
            &lt;span class=&quot;c1&quot;&gt;//do something with x, y and z&lt;/span&gt;
            &lt;span class=&quot;nf&quot;&gt;print&lt;/span&gt;&lt;span class=&quot;p&quot;&gt;(&lt;/span&gt;&lt;span class=&quot;s&quot;&gt;&quot;&lt;/span&gt;&lt;span class=&quot;se&quot;&gt;\(&lt;/span&gt;&lt;span class=&quot;n&quot;&gt;x&lt;/span&gt;&lt;span class=&quot;p&quot;&gt;,&lt;/span&gt; &lt;span class=&quot;n&quot;&gt;y&lt;/span&gt;&lt;span class=&quot;p&quot;&gt;,&lt;/span&gt; &lt;span class=&quot;n&quot;&gt;z&lt;/span&gt;&lt;span class=&quot;se&quot;&gt;)&lt;/span&gt;&lt;span class=&quot;s&quot;&gt;&quot;&lt;/span&gt;&lt;span class=&quot;p&quot;&gt;)&lt;/span&gt;
        &lt;span class=&quot;p&quot;&gt;}&lt;/span&gt;
    &lt;span class=&quot;p&quot;&gt;}&lt;/span&gt;
&lt;span class=&quot;p&quot;&gt;}&lt;/span&gt;
&lt;/code&gt;&lt;/pre&gt;&lt;/div&gt;
&lt;p&gt;Assuming we need &lt;code&gt;z&lt;/code&gt; to be less than &lt;code&gt;4&lt;/code&gt; - code seems pretty normal. Let’s rewrite it to use &lt;code&gt;where&lt;/code&gt; clause&lt;/p&gt;
&lt;div class=&quot;highlight&quot;&gt;&lt;pre&gt;&lt;code class=&quot;language-swift&quot; data-lang=&quot;swift&quot;&gt;&lt;span class=&quot;kd&quot;&gt;func&lt;/span&gt; &lt;span class=&quot;nf&quot;&gt;whereClause&lt;/span&gt;&lt;span class=&quot;p&quot;&gt;(&lt;/span&gt;&lt;span class=&quot;nv&quot;&gt;x&lt;/span&gt;&lt;span class=&quot;p&quot;&gt;:&lt;/span&gt; &lt;span class=&quot;kt&quot;&gt;Int&lt;/span&gt;&lt;span class=&quot;p&quot;&gt;?,&lt;/span&gt; &lt;span class=&quot;nv&quot;&gt;y&lt;/span&gt;&lt;span class=&quot;p&quot;&gt;:&lt;/span&gt; &lt;span class=&quot;kt&quot;&gt;Int&lt;/span&gt;&lt;span class=&quot;p&quot;&gt;?,&lt;/span&gt; &lt;span class=&quot;nv&quot;&gt;z&lt;/span&gt;&lt;span class=&quot;p&quot;&gt;:&lt;/span&gt; &lt;span class=&quot;kt&quot;&gt;Int&lt;/span&gt;&lt;span class=&quot;p&quot;&gt;?)&lt;/span&gt; &lt;span class=&quot;p&quot;&gt;{&lt;/span&gt;
    &lt;span class=&quot;k&quot;&gt;if&lt;/span&gt; &lt;span class=&quot;k&quot;&gt;let&lt;/span&gt; &lt;span class=&quot;nv&quot;&gt;x&lt;/span&gt; &lt;span class=&quot;o&quot;&gt;=&lt;/span&gt; &lt;span class=&quot;n&quot;&gt;x&lt;/span&gt;&lt;span class=&quot;p&quot;&gt;,&lt;/span&gt; &lt;span class=&quot;n&quot;&gt;y&lt;/span&gt; &lt;span class=&quot;o&quot;&gt;=&lt;/span&gt; &lt;span class=&quot;n&quot;&gt;y&lt;/span&gt;&lt;span class=&quot;p&quot;&gt;,&lt;/span&gt; &lt;span class=&quot;n&quot;&gt;z&lt;/span&gt; &lt;span class=&quot;o&quot;&gt;=&lt;/span&gt; &lt;span class=&quot;n&quot;&gt;z&lt;/span&gt; &lt;span class=&quot;k&quot;&gt;where&lt;/span&gt; &lt;span class=&quot;n&quot;&gt;z&lt;/span&gt; &lt;span class=&quot;o&quot;&gt;&amp;lt;&lt;/span&gt; &lt;span class=&quot;mi&quot;&gt;4&lt;/span&gt; &lt;span class=&quot;p&quot;&gt;{&lt;/span&gt;
        &lt;span class=&quot;c1&quot;&gt;//do something with x, y and z&lt;/span&gt;
        &lt;span class=&quot;nf&quot;&gt;print&lt;/span&gt;&lt;span class=&quot;p&quot;&gt;(&lt;/span&gt;&lt;span class=&quot;s&quot;&gt;&quot;&lt;/span&gt;&lt;span class=&quot;se&quot;&gt;\(&lt;/span&gt;&lt;span class=&quot;n&quot;&gt;x&lt;/span&gt;&lt;span class=&quot;p&quot;&gt;,&lt;/span&gt; &lt;span class=&quot;n&quot;&gt;y&lt;/span&gt;&lt;span class=&quot;p&quot;&gt;,&lt;/span&gt; &lt;span class=&quot;n&quot;&gt;z&lt;/span&gt;&lt;span class=&quot;se&quot;&gt;)&lt;/span&gt;&lt;span class=&quot;s&quot;&gt;&quot;&lt;/span&gt;&lt;span class=&quot;p&quot;&gt;)&lt;/span&gt;
    &lt;span class=&quot;p&quot;&gt;}&lt;/span&gt;
&lt;span class=&quot;p&quot;&gt;}&lt;/span&gt;
&lt;/code&gt;&lt;/pre&gt;&lt;/div&gt;
&lt;p&gt;One less level of code indentation and a bit cleaner code. You can add one where clause per each &lt;code&gt;let&lt;/code&gt; statement&lt;/p&gt;
&lt;div class=&quot;highlight&quot;&gt;&lt;pre&gt;&lt;code class=&quot;language-swift&quot; data-lang=&quot;swift&quot;&gt;&lt;span class=&quot;kd&quot;&gt;func&lt;/span&gt; &lt;span class=&quot;nf&quot;&gt;multipleWhereClause&lt;/span&gt;&lt;span class=&quot;p&quot;&gt;(&lt;/span&gt;&lt;span class=&quot;nv&quot;&gt;x&lt;/span&gt;&lt;span class=&quot;p&quot;&gt;:&lt;/span&gt; &lt;span class=&quot;kt&quot;&gt;Int&lt;/span&gt;&lt;span class=&quot;p&quot;&gt;?,&lt;/span&gt; &lt;span class=&quot;nv&quot;&gt;y&lt;/span&gt;&lt;span class=&quot;p&quot;&gt;:&lt;/span&gt; &lt;span class=&quot;kt&quot;&gt;Int&lt;/span&gt;&lt;span class=&quot;p&quot;&gt;?,&lt;/span&gt; &lt;span class=&quot;nv&quot;&gt;z&lt;/span&gt;&lt;span class=&quot;p&quot;&gt;:&lt;/span&gt; &lt;span class=&quot;kt&quot;&gt;Int&lt;/span&gt;&lt;span class=&quot;p&quot;&gt;?)&lt;/span&gt; &lt;span class=&quot;p&quot;&gt;{&lt;/span&gt;
    &lt;span class=&quot;k&quot;&gt;if&lt;/span&gt; &lt;span class=&quot;k&quot;&gt;let&lt;/span&gt; &lt;span class=&quot;nv&quot;&gt;x&lt;/span&gt; &lt;span class=&quot;o&quot;&gt;=&lt;/span&gt; &lt;span class=&quot;n&quot;&gt;x&lt;/span&gt; &lt;span class=&quot;k&quot;&gt;where&lt;/span&gt; &lt;span class=&quot;n&quot;&gt;x&lt;/span&gt; &lt;span class=&quot;o&quot;&gt;&amp;lt;&lt;/span&gt; &lt;span class=&quot;mi&quot;&gt;2&lt;/span&gt;&lt;span class=&quot;p&quot;&gt;,&lt;/span&gt;
       &lt;span class=&quot;k&quot;&gt;let&lt;/span&gt; &lt;span class=&quot;nv&quot;&gt;y&lt;/span&gt; &lt;span class=&quot;o&quot;&gt;=&lt;/span&gt; &lt;span class=&quot;n&quot;&gt;y&lt;/span&gt; &lt;span class=&quot;k&quot;&gt;where&lt;/span&gt; &lt;span class=&quot;n&quot;&gt;y&lt;/span&gt; &lt;span class=&quot;o&quot;&gt;&amp;lt;&lt;/span&gt; &lt;span class=&quot;mi&quot;&gt;3&lt;/span&gt;&lt;span class=&quot;p&quot;&gt;,&lt;/span&gt;
       &lt;span class=&quot;k&quot;&gt;let&lt;/span&gt; &lt;span class=&quot;nv&quot;&gt;z&lt;/span&gt; &lt;span class=&quot;o&quot;&gt;=&lt;/span&gt; &lt;span class=&quot;n&quot;&gt;z&lt;/span&gt; &lt;span class=&quot;k&quot;&gt;where&lt;/span&gt; &lt;span class=&quot;n&quot;&gt;z&lt;/span&gt; &lt;span class=&quot;o&quot;&gt;&amp;lt;&lt;/span&gt; &lt;span class=&quot;mi&quot;&gt;4&lt;/span&gt; &lt;span class=&quot;p&quot;&gt;{&lt;/span&gt;
            &lt;span class=&quot;c1&quot;&gt;//do something with x, y and z&lt;/span&gt;
            &lt;span class=&quot;nf&quot;&gt;print&lt;/span&gt;&lt;span class=&quot;p&quot;&gt;(&lt;/span&gt;&lt;span class=&quot;s&quot;&gt;&quot;&lt;/span&gt;&lt;span class=&quot;se&quot;&gt;\(&lt;/span&gt;&lt;span class=&quot;n&quot;&gt;x&lt;/span&gt;&lt;span class=&quot;p&quot;&gt;,&lt;/span&gt; &lt;span class=&quot;n&quot;&gt;y&lt;/span&gt;&lt;span class=&quot;p&quot;&gt;,&lt;/span&gt; &lt;span class=&quot;n&quot;&gt;z&lt;/span&gt;&lt;span class=&quot;se&quot;&gt;)&lt;/span&gt;&lt;span class=&quot;s&quot;&gt;&quot;&lt;/span&gt;&lt;span class=&quot;p&quot;&gt;)&lt;/span&gt;
    &lt;span class=&quot;p&quot;&gt;}&lt;/span&gt;
&lt;span class=&quot;p&quot;&gt;}&lt;/span&gt;
&lt;/code&gt;&lt;/pre&gt;&lt;/div&gt;
&lt;p&gt;which acts exactly the same as&lt;/p&gt;
&lt;div class=&quot;highlight&quot;&gt;&lt;pre&gt;&lt;code class=&quot;language-swift&quot; data-lang=&quot;swift&quot;&gt;&lt;span class=&quot;kd&quot;&gt;func&lt;/span&gt; &lt;span class=&quot;nf&quot;&gt;multipleWhereClause2&lt;/span&gt;&lt;span class=&quot;p&quot;&gt;(&lt;/span&gt;&lt;span class=&quot;nv&quot;&gt;x&lt;/span&gt;&lt;span class=&quot;p&quot;&gt;:&lt;/span&gt; &lt;span class=&quot;kt&quot;&gt;Int&lt;/span&gt;&lt;span class=&quot;p&quot;&gt;?,&lt;/span&gt; &lt;span class=&quot;nv&quot;&gt;y&lt;/span&gt;&lt;span class=&quot;p&quot;&gt;:&lt;/span&gt; &lt;span class=&quot;kt&quot;&gt;Int&lt;/span&gt;&lt;span class=&quot;p&quot;&gt;?,&lt;/span&gt; &lt;span class=&quot;nv&quot;&gt;z&lt;/span&gt;&lt;span class=&quot;p&quot;&gt;:&lt;/span&gt; &lt;span class=&quot;kt&quot;&gt;Int&lt;/span&gt;&lt;span class=&quot;p&quot;&gt;?)&lt;/span&gt; &lt;span class=&quot;p&quot;&gt;{&lt;/span&gt;
    &lt;span class=&quot;k&quot;&gt;if&lt;/span&gt; &lt;span class=&quot;k&quot;&gt;let&lt;/span&gt; &lt;span class=&quot;nv&quot;&gt;x&lt;/span&gt; &lt;span class=&quot;o&quot;&gt;=&lt;/span&gt; &lt;span class=&quot;n&quot;&gt;x&lt;/span&gt;&lt;span class=&quot;p&quot;&gt;,&lt;/span&gt; &lt;span class=&quot;n&quot;&gt;y&lt;/span&gt; &lt;span class=&quot;o&quot;&gt;=&lt;/span&gt; &lt;span class=&quot;n&quot;&gt;y&lt;/span&gt;&lt;span class=&quot;p&quot;&gt;,&lt;/span&gt; &lt;span class=&quot;n&quot;&gt;z&lt;/span&gt; &lt;span class=&quot;o&quot;&gt;=&lt;/span&gt; &lt;span class=&quot;n&quot;&gt;z&lt;/span&gt; &lt;span class=&quot;k&quot;&gt;where&lt;/span&gt; &lt;span class=&quot;n&quot;&gt;x&lt;/span&gt; &lt;span class=&quot;o&quot;&gt;&amp;lt;&lt;/span&gt; &lt;span class=&quot;mi&quot;&gt;2&lt;/span&gt; &lt;span class=&quot;o&quot;&gt;&amp;amp;&amp;amp;&lt;/span&gt; &lt;span class=&quot;n&quot;&gt;y&lt;/span&gt; &lt;span class=&quot;o&quot;&gt;&amp;lt;&lt;/span&gt; &lt;span class=&quot;mi&quot;&gt;3&lt;/span&gt; &lt;span class=&quot;o&quot;&gt;&amp;amp;&amp;amp;&lt;/span&gt; &lt;span class=&quot;n&quot;&gt;z&lt;/span&gt; &lt;span class=&quot;o&quot;&gt;&amp;lt;&lt;/span&gt; &lt;span class=&quot;mi&quot;&gt;4&lt;/span&gt; &lt;span class=&quot;p&quot;&gt;{&lt;/span&gt;
        &lt;span class=&quot;c1&quot;&gt;//do something with x, y and z&lt;/span&gt;
        &lt;span class=&quot;nf&quot;&gt;print&lt;/span&gt;&lt;span class=&quot;p&quot;&gt;(&lt;/span&gt;&lt;span class=&quot;s&quot;&gt;&quot;&lt;/span&gt;&lt;span class=&quot;se&quot;&gt;\(&lt;/span&gt;&lt;span class=&quot;n&quot;&gt;x&lt;/span&gt;&lt;span class=&quot;p&quot;&gt;,&lt;/span&gt; &lt;span class=&quot;n&quot;&gt;y&lt;/span&gt;&lt;span class=&quot;p&quot;&gt;,&lt;/span&gt; &lt;span class=&quot;n&quot;&gt;z&lt;/span&gt;&lt;span class=&quot;se&quot;&gt;)&lt;/span&gt;&lt;span class=&quot;s&quot;&gt;&quot;&lt;/span&gt;&lt;span class=&quot;p&quot;&gt;)&lt;/span&gt;
    &lt;span class=&quot;p&quot;&gt;}&lt;/span&gt;
&lt;span class=&quot;p&quot;&gt;}&lt;/span&gt;
&lt;/code&gt;&lt;/pre&gt;&lt;/div&gt;
&lt;p&gt;Which version to use? It’s mostly a matter of preference and depends what you think is easier to read.&lt;/p&gt;

&lt;p&gt;I prefer version #1, as it’s a bit more explicit and for the same reason I advise you do the same – if you can add more readability by spending few more seconds on typing additional &lt;code&gt;let&lt;/code&gt; statements – do so, people reading your code later will be grateful.&lt;/p&gt;

&lt;p&gt;One important note to remember, is that assignment and unwrapping happens before the condition in &lt;code&gt;where&lt;/code&gt; clause is checked. &lt;br&gt;
This means, if your condition is unrelated to unwrapped variables – it might be better to check the condition first. Why?&lt;/p&gt;
&lt;div class=&quot;highlight&quot;&gt;&lt;pre&gt;&lt;code class=&quot;language-swift&quot; data-lang=&quot;swift&quot;&gt;&lt;span class=&quot;kd&quot;&gt;func&lt;/span&gt; &lt;span class=&quot;nf&quot;&gt;expensiveFunction&lt;/span&gt;&lt;span class=&quot;p&quot;&gt;(&lt;/span&gt;&lt;span class=&quot;nv&quot;&gt;startWith&lt;/span&gt;&lt;span class=&quot;p&quot;&gt;:&lt;/span&gt; &lt;span class=&quot;kt&quot;&gt;Int&lt;/span&gt;&lt;span class=&quot;p&quot;&gt;)&lt;/span&gt; &lt;span class=&quot;o&quot;&gt;-&amp;gt;&lt;/span&gt; &lt;span class=&quot;kt&quot;&gt;Int&lt;/span&gt;&lt;span class=&quot;p&quot;&gt;?&lt;/span&gt; &lt;span class=&quot;p&quot;&gt;{&lt;/span&gt;
    &lt;span class=&quot;c1&quot;&gt;//despite what you see here&lt;/span&gt;
    &lt;span class=&quot;c1&quot;&gt;//it is really expensive to call this function!&lt;/span&gt;
    &lt;span class=&quot;k&quot;&gt;return&lt;/span&gt; &lt;span class=&quot;n&quot;&gt;startWith&lt;/span&gt; &lt;span class=&quot;o&quot;&gt;*&lt;/span&gt; &lt;span class=&quot;mi&quot;&gt;2&lt;/span&gt;
&lt;span class=&quot;p&quot;&gt;}&lt;/span&gt;

&lt;span class=&quot;kd&quot;&gt;func&lt;/span&gt; &lt;span class=&quot;nf&quot;&gt;isTodayThursday&lt;/span&gt;&lt;span class=&quot;p&quot;&gt;()&lt;/span&gt; &lt;span class=&quot;o&quot;&gt;-&amp;gt;&lt;/span&gt; &lt;span class=&quot;kt&quot;&gt;Bool&lt;/span&gt; &lt;span class=&quot;p&quot;&gt;{&lt;/span&gt;
    &lt;span class=&quot;c1&quot;&gt;//I&#39;m writing it on Tuesday, so we can optimize ;)&lt;/span&gt;
    &lt;span class=&quot;k&quot;&gt;return&lt;/span&gt; &lt;span class=&quot;kc&quot;&gt;false&lt;/span&gt;
&lt;span class=&quot;p&quot;&gt;}&lt;/span&gt;

&lt;span class=&quot;kd&quot;&gt;func&lt;/span&gt; &lt;span class=&quot;nf&quot;&gt;expensiveUnwrapping&lt;/span&gt;&lt;span class=&quot;p&quot;&gt;()&lt;/span&gt; &lt;span class=&quot;p&quot;&gt;{&lt;/span&gt;
    &lt;span class=&quot;k&quot;&gt;if&lt;/span&gt; &lt;span class=&quot;k&quot;&gt;let&lt;/span&gt; &lt;span class=&quot;nv&quot;&gt;x&lt;/span&gt; &lt;span class=&quot;o&quot;&gt;=&lt;/span&gt; &lt;span class=&quot;nf&quot;&gt;expensiveFunction&lt;/span&gt;&lt;span class=&quot;p&quot;&gt;(&lt;/span&gt;&lt;span class=&quot;mi&quot;&gt;2&lt;/span&gt;&lt;span class=&quot;p&quot;&gt;),&lt;/span&gt; &lt;span class=&quot;n&quot;&gt;y&lt;/span&gt; &lt;span class=&quot;o&quot;&gt;=&lt;/span&gt; &lt;span class=&quot;nf&quot;&gt;expensiveFunction&lt;/span&gt;&lt;span class=&quot;p&quot;&gt;(&lt;/span&gt;&lt;span class=&quot;mi&quot;&gt;5&lt;/span&gt;&lt;span class=&quot;p&quot;&gt;)&lt;/span&gt; &lt;span class=&quot;k&quot;&gt;where&lt;/span&gt; &lt;span class=&quot;nf&quot;&gt;isTodayThursday&lt;/span&gt;&lt;span class=&quot;p&quot;&gt;()&lt;/span&gt; &lt;span class=&quot;p&quot;&gt;{&lt;/span&gt;
        &lt;span class=&quot;nf&quot;&gt;print&lt;/span&gt;&lt;span class=&quot;p&quot;&gt;(&lt;/span&gt;&lt;span class=&quot;s&quot;&gt;&quot;&lt;/span&gt;&lt;span class=&quot;se&quot;&gt;\(&lt;/span&gt;&lt;span class=&quot;n&quot;&gt;x&lt;/span&gt;&lt;span class=&quot;p&quot;&gt;,&lt;/span&gt; &lt;span class=&quot;n&quot;&gt;y&lt;/span&gt;&lt;span class=&quot;se&quot;&gt;)&lt;/span&gt;&lt;span class=&quot;s&quot;&gt;&quot;&lt;/span&gt;&lt;span class=&quot;p&quot;&gt;)&lt;/span&gt;
    &lt;span class=&quot;p&quot;&gt;}&lt;/span&gt;
&lt;span class=&quot;p&quot;&gt;}&lt;/span&gt;
&lt;/code&gt;&lt;/pre&gt;&lt;/div&gt;
&lt;p&gt;It matters how do we get our optional values. If, as in the example above, they come from a function that is really expensive to call – it would be smart to call it only if we can be sure that returned value will actually be used.&lt;/p&gt;

&lt;p&gt;In the example above, our expensive function is being called twice, even though we don’t even get to use &lt;code&gt;x&lt;/code&gt; and &lt;code&gt;y&lt;/code&gt; variables.&lt;/p&gt;

&lt;p&gt;For similar cases, you might use the fact that we are allowed to use one logic statement (outside of &lt;code&gt;where&lt;/code&gt; clause) as long as it’s the first clause in the &lt;code&gt;if let&lt;/code&gt; statement&lt;/p&gt;
&lt;div class=&quot;highlight&quot;&gt;&lt;pre&gt;&lt;code class=&quot;language-swift&quot; data-lang=&quot;swift&quot;&gt;&lt;span class=&quot;kd&quot;&gt;func&lt;/span&gt; &lt;span class=&quot;nf&quot;&gt;unexpensiveUnwrapping&lt;/span&gt;&lt;span class=&quot;p&quot;&gt;()&lt;/span&gt; &lt;span class=&quot;p&quot;&gt;{&lt;/span&gt;
    &lt;span class=&quot;k&quot;&gt;if&lt;/span&gt; &lt;span class=&quot;nf&quot;&gt;isTodayThursday&lt;/span&gt;&lt;span class=&quot;p&quot;&gt;(),&lt;/span&gt; &lt;span class=&quot;k&quot;&gt;let&lt;/span&gt; &lt;span class=&quot;nv&quot;&gt;x&lt;/span&gt; &lt;span class=&quot;o&quot;&gt;=&lt;/span&gt; &lt;span class=&quot;nf&quot;&gt;expensiveFunction&lt;/span&gt;&lt;span class=&quot;p&quot;&gt;(&lt;/span&gt;&lt;span class=&quot;mi&quot;&gt;2&lt;/span&gt;&lt;span class=&quot;p&quot;&gt;),&lt;/span&gt; &lt;span class=&quot;n&quot;&gt;y&lt;/span&gt; &lt;span class=&quot;o&quot;&gt;=&lt;/span&gt; &lt;span class=&quot;nf&quot;&gt;expensiveFunction&lt;/span&gt;&lt;span class=&quot;p&quot;&gt;(&lt;/span&gt;&lt;span class=&quot;mi&quot;&gt;5&lt;/span&gt;&lt;span class=&quot;p&quot;&gt;)&lt;/span&gt; &lt;span class=&quot;p&quot;&gt;{&lt;/span&gt;
        &lt;span class=&quot;nf&quot;&gt;print&lt;/span&gt;&lt;span class=&quot;p&quot;&gt;(&lt;/span&gt;&lt;span class=&quot;s&quot;&gt;&quot;&lt;/span&gt;&lt;span class=&quot;se&quot;&gt;\(&lt;/span&gt;&lt;span class=&quot;n&quot;&gt;x&lt;/span&gt;&lt;span class=&quot;p&quot;&gt;,&lt;/span&gt; &lt;span class=&quot;n&quot;&gt;y&lt;/span&gt;&lt;span class=&quot;se&quot;&gt;)&lt;/span&gt;&lt;span class=&quot;s&quot;&gt;&quot;&lt;/span&gt;&lt;span class=&quot;p&quot;&gt;)&lt;/span&gt;
    &lt;span class=&quot;p&quot;&gt;}&lt;/span&gt;
&lt;span class=&quot;p&quot;&gt;}&lt;/span&gt;
&lt;/code&gt;&lt;/pre&gt;&lt;/div&gt;
&lt;p&gt;This way our expensive functions will be called only if our initial logic clause is &lt;code&gt;true&lt;/code&gt; (according to answer by Chris Lattner on &lt;a href=&quot;https://groups.google.com/forum/#!topic/swift-language/TKQ2IOXR6AQ&quot;&gt;google groups&lt;/a&gt;).&lt;/p&gt;

&lt;p&gt;Adding one logic clause at the beginning, works exactly the same with &lt;code&gt;guard&lt;/code&gt; statement&lt;/p&gt;
&lt;div class=&quot;highlight&quot;&gt;&lt;pre&gt;&lt;code class=&quot;language-swift&quot; data-lang=&quot;swift&quot;&gt;&lt;span class=&quot;kd&quot;&gt;func&lt;/span&gt; &lt;span class=&quot;nf&quot;&gt;guardUnexpensive&lt;/span&gt;&lt;span class=&quot;p&quot;&gt;()&lt;/span&gt; &lt;span class=&quot;p&quot;&gt;{&lt;/span&gt;
    &lt;span class=&quot;k&quot;&gt;guard&lt;/span&gt; &lt;span class=&quot;nf&quot;&gt;isTodayThursday&lt;/span&gt;&lt;span class=&quot;p&quot;&gt;(),&lt;/span&gt; &lt;span class=&quot;k&quot;&gt;let&lt;/span&gt; &lt;span class=&quot;nv&quot;&gt;x&lt;/span&gt; &lt;span class=&quot;o&quot;&gt;=&lt;/span&gt; &lt;span class=&quot;nf&quot;&gt;expensiveFunction&lt;/span&gt;&lt;span class=&quot;p&quot;&gt;(&lt;/span&gt;&lt;span class=&quot;mi&quot;&gt;2&lt;/span&gt;&lt;span class=&quot;p&quot;&gt;),&lt;/span&gt; &lt;span class=&quot;n&quot;&gt;y&lt;/span&gt; &lt;span class=&quot;o&quot;&gt;=&lt;/span&gt; &lt;span class=&quot;nf&quot;&gt;expensiveFunction&lt;/span&gt;&lt;span class=&quot;p&quot;&gt;(&lt;/span&gt;&lt;span class=&quot;mi&quot;&gt;5&lt;/span&gt;&lt;span class=&quot;p&quot;&gt;)&lt;/span&gt; &lt;span class=&quot;k&quot;&gt;else&lt;/span&gt; &lt;span class=&quot;p&quot;&gt;{&lt;/span&gt;
        &lt;span class=&quot;k&quot;&gt;return&lt;/span&gt;
    &lt;span class=&quot;p&quot;&gt;}&lt;/span&gt;
    &lt;span class=&quot;nf&quot;&gt;print&lt;/span&gt;&lt;span class=&quot;p&quot;&gt;(&lt;/span&gt;&lt;span class=&quot;s&quot;&gt;&quot;&lt;/span&gt;&lt;span class=&quot;se&quot;&gt;\(&lt;/span&gt;&lt;span class=&quot;n&quot;&gt;x&lt;/span&gt;&lt;span class=&quot;p&quot;&gt;,&lt;/span&gt; &lt;span class=&quot;n&quot;&gt;y&lt;/span&gt;&lt;span class=&quot;se&quot;&gt;)&lt;/span&gt;&lt;span class=&quot;s&quot;&gt;&quot;&lt;/span&gt;&lt;span class=&quot;p&quot;&gt;)&lt;/span&gt;
&lt;span class=&quot;p&quot;&gt;}&lt;/span&gt;
&lt;/code&gt;&lt;/pre&gt;&lt;/div&gt;
&lt;p&gt;That’s it for now. In one of the next articles I will go into pattern matching and I’ll explain why following statements produce exactly same results. Stay tuned!&lt;/p&gt;
&lt;div class=&quot;highlight&quot;&gt;&lt;pre&gt;&lt;code class=&quot;language-swift&quot; data-lang=&quot;swift&quot;&gt;&lt;span class=&quot;k&quot;&gt;if&lt;/span&gt; &lt;span class=&quot;k&quot;&gt;let&lt;/span&gt; &lt;span class=&quot;nv&quot;&gt;x&lt;/span&gt; &lt;span class=&quot;o&quot;&gt;=&lt;/span&gt; &lt;span class=&quot;n&quot;&gt;x&lt;/span&gt; &lt;span class=&quot;p&quot;&gt;{&lt;/span&gt;
    &lt;span class=&quot;nf&quot;&gt;printSomething&lt;/span&gt;&lt;span class=&quot;p&quot;&gt;()&lt;/span&gt;
&lt;span class=&quot;p&quot;&gt;}&lt;/span&gt;

&lt;span class=&quot;k&quot;&gt;if&lt;/span&gt; &lt;span class=&quot;k&quot;&gt;case&lt;/span&gt; &lt;span class=&quot;k&quot;&gt;let&lt;/span&gt; &lt;span class=&quot;nv&quot;&gt;x&lt;/span&gt;&lt;span class=&quot;p&quot;&gt;?&lt;/span&gt; &lt;span class=&quot;o&quot;&gt;=&lt;/span&gt; &lt;span class=&quot;n&quot;&gt;x&lt;/span&gt; &lt;span class=&quot;p&quot;&gt;{&lt;/span&gt;
    &lt;span class=&quot;nf&quot;&gt;printSomething&lt;/span&gt;&lt;span class=&quot;p&quot;&gt;()&lt;/span&gt;
&lt;span class=&quot;p&quot;&gt;}&lt;/span&gt;

&lt;span class=&quot;k&quot;&gt;if&lt;/span&gt; &lt;span class=&quot;k&quot;&gt;case&lt;/span&gt; &lt;span class=&quot;o&quot;&gt;.&lt;/span&gt;&lt;span class=&quot;kt&quot;&gt;Some&lt;/span&gt;&lt;span class=&quot;p&quot;&gt;(&lt;/span&gt;&lt;span class=&quot;k&quot;&gt;let&lt;/span&gt; &lt;span class=&quot;nv&quot;&gt;x&lt;/span&gt;&lt;span class=&quot;p&quot;&gt;)&lt;/span&gt; &lt;span class=&quot;o&quot;&gt;=&lt;/span&gt; &lt;span class=&quot;n&quot;&gt;x&lt;/span&gt; &lt;span class=&quot;p&quot;&gt;{&lt;/span&gt;
    &lt;span class=&quot;nf&quot;&gt;printSomething&lt;/span&gt;&lt;span class=&quot;p&quot;&gt;()&lt;/span&gt;
&lt;span class=&quot;p&quot;&gt;}&lt;/span&gt;
&lt;/code&gt;&lt;/pre&gt;&lt;/div&gt;</description>
        <pubDate>Mon, 09 May 2016 08:00:00 -0400</pubDate>
        <link>http://iosdev.nyc/blog/if-let-where/</link>
        <guid isPermaLink="true">http://iosdev.nyc/blog/if-let-where/</guid>
      </item>
    
      <item>
        <title>Let and guard statements in Swift</title>
        <description>&lt;p&gt;&lt;strong&gt;Update, 07 Feb 2017&lt;/strong&gt;&lt;br&gt;
As of Swift 3, some of the code below may not work properly anymore. To see what changed, read &lt;a href=&quot;/blog/let-guard-pyramid-of-doom-swift-3/&quot;&gt;Pyramid of Doom Updated (Swift 3)&lt;/a&gt;.&lt;/p&gt;

&lt;hr&gt;

&lt;p&gt;&lt;strong&gt;Original Post&lt;/strong&gt;&lt;/p&gt;

&lt;p&gt;Swift 2 was announced in June, soon to be a year ago. Still, some of the concepts it introduced are new to many iOS developers – especially the ones who keep using ObjC as their #1 language and are only starting to learn Swift.&lt;/p&gt;

&lt;p&gt;One of the new things introduced in Swift 2 is guard statement, which I think finally solves Swift’s pyramid of doom (or what I called &lt;em&gt;“let indentation hell”&lt;/em&gt; – that’s what you get when you are nesting &lt;a href=&quot;https://developer.apple.com/library/prerelease/content/documentation/Swift/Conceptual/Swift_Programming_Language/TheBasics.html&quot;&gt;optional binding&lt;/a&gt; statements one inside another).&lt;/p&gt;

&lt;p&gt;First, let’s take a look at hypothetical code of setting an author on a book, in Swift &amp;lt; 1.2&lt;/p&gt;
&lt;div class=&quot;highlight&quot;&gt;&lt;pre&gt;&lt;code class=&quot;language-swift&quot; data-lang=&quot;swift&quot;&gt;&lt;span class=&quot;kd&quot;&gt;func&lt;/span&gt; &lt;span class=&quot;nf&quot;&gt;letIndentationHell&lt;/span&gt;&lt;span class=&quot;p&quot;&gt;(&lt;/span&gt;&lt;span class=&quot;nv&quot;&gt;foo&lt;/span&gt;&lt;span class=&quot;p&quot;&gt;:&lt;/span&gt; &lt;span class=&quot;kt&quot;&gt;Book&lt;/span&gt;&lt;span class=&quot;p&quot;&gt;?,&lt;/span&gt; &lt;span class=&quot;nv&quot;&gt;bar&lt;/span&gt;&lt;span class=&quot;p&quot;&gt;:&lt;/span&gt; &lt;span class=&quot;kt&quot;&gt;Author&lt;/span&gt;&lt;span class=&quot;p&quot;&gt;?)&lt;/span&gt; &lt;span class=&quot;p&quot;&gt;{&lt;/span&gt;
    &lt;span class=&quot;k&quot;&gt;if&lt;/span&gt; &lt;span class=&quot;k&quot;&gt;let&lt;/span&gt; &lt;span class=&quot;nv&quot;&gt;book&lt;/span&gt; &lt;span class=&quot;o&quot;&gt;=&lt;/span&gt; &lt;span class=&quot;n&quot;&gt;foo&lt;/span&gt; &lt;span class=&quot;p&quot;&gt;{&lt;/span&gt;
        &lt;span class=&quot;k&quot;&gt;if&lt;/span&gt; &lt;span class=&quot;k&quot;&gt;let&lt;/span&gt; &lt;span class=&quot;nv&quot;&gt;author&lt;/span&gt; &lt;span class=&quot;o&quot;&gt;=&lt;/span&gt; &lt;span class=&quot;n&quot;&gt;bar&lt;/span&gt; &lt;span class=&quot;p&quot;&gt;{&lt;/span&gt;
            &lt;span class=&quot;n&quot;&gt;book&lt;/span&gt;&lt;span class=&quot;o&quot;&gt;.&lt;/span&gt;&lt;span class=&quot;nf&quot;&gt;setAuthor&lt;/span&gt;&lt;span class=&quot;p&quot;&gt;(&lt;/span&gt;&lt;span class=&quot;n&quot;&gt;author&lt;/span&gt;&lt;span class=&quot;p&quot;&gt;)&lt;/span&gt;
        &lt;span class=&quot;p&quot;&gt;}&lt;/span&gt;
    &lt;span class=&quot;p&quot;&gt;}&lt;/span&gt;
&lt;span class=&quot;p&quot;&gt;}&lt;/span&gt;
&lt;/code&gt;&lt;/pre&gt;&lt;/div&gt;
&lt;p&gt;That was one of the things that really terrified me when I first started using Swift 1.0 – and when you were also using ObjC-bridged code, this nesting could have been even deeper.&lt;/p&gt;

&lt;p&gt;Swift 1.2 allowed us to bind multiple optionals in one statement&lt;/p&gt;
&lt;div class=&quot;highlight&quot;&gt;&lt;pre&gt;&lt;code class=&quot;language-swift&quot; data-lang=&quot;swift&quot;&gt;&lt;span class=&quot;kd&quot;&gt;func&lt;/span&gt; &lt;span class=&quot;nf&quot;&gt;multipleBind&lt;/span&gt;&lt;span class=&quot;p&quot;&gt;(&lt;/span&gt;&lt;span class=&quot;nv&quot;&gt;foo&lt;/span&gt;&lt;span class=&quot;p&quot;&gt;:&lt;/span&gt; &lt;span class=&quot;kt&quot;&gt;Book&lt;/span&gt;&lt;span class=&quot;p&quot;&gt;?,&lt;/span&gt; &lt;span class=&quot;nv&quot;&gt;bar&lt;/span&gt;&lt;span class=&quot;p&quot;&gt;:&lt;/span&gt; &lt;span class=&quot;kt&quot;&gt;Author&lt;/span&gt;&lt;span class=&quot;p&quot;&gt;?)&lt;/span&gt; &lt;span class=&quot;p&quot;&gt;{&lt;/span&gt;
    &lt;span class=&quot;k&quot;&gt;if&lt;/span&gt; &lt;span class=&quot;k&quot;&gt;let&lt;/span&gt; &lt;span class=&quot;nv&quot;&gt;book&lt;/span&gt; &lt;span class=&quot;o&quot;&gt;=&lt;/span&gt; &lt;span class=&quot;n&quot;&gt;foo&lt;/span&gt;&lt;span class=&quot;p&quot;&gt;,&lt;/span&gt; &lt;span class=&quot;k&quot;&gt;let&lt;/span&gt; &lt;span class=&quot;nv&quot;&gt;author&lt;/span&gt; &lt;span class=&quot;o&quot;&gt;=&lt;/span&gt; &lt;span class=&quot;n&quot;&gt;bar&lt;/span&gt; &lt;span class=&quot;p&quot;&gt;{&lt;/span&gt;
        &lt;span class=&quot;n&quot;&gt;book&lt;/span&gt;&lt;span class=&quot;o&quot;&gt;.&lt;/span&gt;&lt;span class=&quot;nf&quot;&gt;setAuthor&lt;/span&gt;&lt;span class=&quot;p&quot;&gt;(&lt;/span&gt;&lt;span class=&quot;n&quot;&gt;author&lt;/span&gt;&lt;span class=&quot;p&quot;&gt;)&lt;/span&gt;
    &lt;span class=&quot;p&quot;&gt;}&lt;/span&gt;
&lt;span class=&quot;p&quot;&gt;}&lt;/span&gt;
&lt;/code&gt;&lt;/pre&gt;&lt;/div&gt;
&lt;p&gt;That already looks better, but still, it forces you to move most of your function’s body inside indented blocks.&lt;/p&gt;

&lt;p&gt;You could avoid it, but it would require ObjC-style &lt;code&gt;nil&lt;/code&gt; checking, and while it works, I just personally don’t like it as much – Swift was supposed to be better than ObjC, right?&lt;/p&gt;
&lt;div class=&quot;highlight&quot;&gt;&lt;pre&gt;&lt;code class=&quot;language-swift&quot; data-lang=&quot;swift&quot;&gt;&lt;span class=&quot;kd&quot;&gt;func&lt;/span&gt; &lt;span class=&quot;nf&quot;&gt;objcStyle&lt;/span&gt;&lt;span class=&quot;p&quot;&gt;(&lt;/span&gt;&lt;span class=&quot;nv&quot;&gt;foo&lt;/span&gt;&lt;span class=&quot;p&quot;&gt;:&lt;/span&gt; &lt;span class=&quot;kt&quot;&gt;Book&lt;/span&gt;&lt;span class=&quot;p&quot;&gt;?,&lt;/span&gt; &lt;span class=&quot;nv&quot;&gt;bar&lt;/span&gt;&lt;span class=&quot;p&quot;&gt;:&lt;/span&gt; &lt;span class=&quot;kt&quot;&gt;Author&lt;/span&gt;&lt;span class=&quot;p&quot;&gt;?)&lt;/span&gt; &lt;span class=&quot;p&quot;&gt;{&lt;/span&gt;
    &lt;span class=&quot;k&quot;&gt;if&lt;/span&gt; &lt;span class=&quot;p&quot;&gt;(&lt;/span&gt;&lt;span class=&quot;n&quot;&gt;foo&lt;/span&gt; &lt;span class=&quot;o&quot;&gt;==&lt;/span&gt; &lt;span class=&quot;kc&quot;&gt;nil&lt;/span&gt; &lt;span class=&quot;o&quot;&gt;&amp;amp;&amp;amp;&lt;/span&gt; &lt;span class=&quot;n&quot;&gt;bar&lt;/span&gt; &lt;span class=&quot;o&quot;&gt;==&lt;/span&gt; &lt;span class=&quot;kc&quot;&gt;nil&lt;/span&gt;&lt;span class=&quot;p&quot;&gt;)&lt;/span&gt; &lt;span class=&quot;p&quot;&gt;{&lt;/span&gt;
        &lt;span class=&quot;k&quot;&gt;return&lt;/span&gt;
    &lt;span class=&quot;p&quot;&gt;}&lt;/span&gt;
    &lt;span class=&quot;k&quot;&gt;let&lt;/span&gt; &lt;span class=&quot;nv&quot;&gt;book&lt;/span&gt; &lt;span class=&quot;o&quot;&gt;=&lt;/span&gt; &lt;span class=&quot;n&quot;&gt;foo&lt;/span&gt;&lt;span class=&quot;o&quot;&gt;!&lt;/span&gt;
    &lt;span class=&quot;k&quot;&gt;let&lt;/span&gt; &lt;span class=&quot;nv&quot;&gt;author&lt;/span&gt; &lt;span class=&quot;o&quot;&gt;=&lt;/span&gt; &lt;span class=&quot;n&quot;&gt;bar&lt;/span&gt;&lt;span class=&quot;o&quot;&gt;!&lt;/span&gt;
    &lt;span class=&quot;n&quot;&gt;book&lt;/span&gt;&lt;span class=&quot;o&quot;&gt;.&lt;/span&gt;&lt;span class=&quot;nf&quot;&gt;setAuthor&lt;/span&gt;&lt;span class=&quot;p&quot;&gt;(&lt;/span&gt;&lt;span class=&quot;n&quot;&gt;author&lt;/span&gt;&lt;span class=&quot;p&quot;&gt;)&lt;/span&gt;
    &lt;span class=&quot;c1&quot;&gt;// or force unwrap both directly with&lt;/span&gt;
    &lt;span class=&quot;c1&quot;&gt;// foo!.setAuthor(bar!)&lt;/span&gt;
&lt;span class=&quot;p&quot;&gt;}&lt;/span&gt;
&lt;/code&gt;&lt;/pre&gt;&lt;/div&gt;
&lt;p&gt;Function above is longer than it could be and it’s also really easy to write wrong condition for the if statement – actually that’s what I did writing it for the first time for this post.&lt;/p&gt;

&lt;p&gt;If you try the code above and one of the &lt;code&gt;obj1&lt;/code&gt; or &lt;code&gt;obj2&lt;/code&gt; is equal to &lt;code&gt;nil&lt;/code&gt; – you will get an error.&lt;br&gt;
(proper condition is &lt;code&gt;if (obj1 == nil || obj2 == nil)&lt;/code&gt;)&lt;/p&gt;

&lt;p&gt;What Swift 2 introduced is actually a combination of solutions suggested in example #2 and #3 – it’s called guard statement.&lt;/p&gt;
&lt;div class=&quot;highlight&quot;&gt;&lt;pre&gt;&lt;code class=&quot;language-swift&quot; data-lang=&quot;swift&quot;&gt;&lt;span class=&quot;kd&quot;&gt;func&lt;/span&gt; &lt;span class=&quot;nf&quot;&gt;swiftGuardStyle&lt;/span&gt;&lt;span class=&quot;p&quot;&gt;(&lt;/span&gt;&lt;span class=&quot;nv&quot;&gt;foo&lt;/span&gt;&lt;span class=&quot;p&quot;&gt;:&lt;/span&gt; &lt;span class=&quot;kt&quot;&gt;Book&lt;/span&gt;&lt;span class=&quot;p&quot;&gt;?,&lt;/span&gt; &lt;span class=&quot;nv&quot;&gt;bar&lt;/span&gt;&lt;span class=&quot;p&quot;&gt;:&lt;/span&gt; &lt;span class=&quot;kt&quot;&gt;Author&lt;/span&gt;&lt;span class=&quot;p&quot;&gt;?)&lt;/span&gt; &lt;span class=&quot;p&quot;&gt;{&lt;/span&gt;
    &lt;span class=&quot;k&quot;&gt;guard&lt;/span&gt; &lt;span class=&quot;k&quot;&gt;let&lt;/span&gt; &lt;span class=&quot;nv&quot;&gt;book&lt;/span&gt; &lt;span class=&quot;o&quot;&gt;=&lt;/span&gt; &lt;span class=&quot;n&quot;&gt;foo&lt;/span&gt;&lt;span class=&quot;p&quot;&gt;,&lt;/span&gt; &lt;span class=&quot;n&quot;&gt;author&lt;/span&gt; &lt;span class=&quot;o&quot;&gt;=&lt;/span&gt; &lt;span class=&quot;n&quot;&gt;bar&lt;/span&gt; &lt;span class=&quot;k&quot;&gt;else&lt;/span&gt; &lt;span class=&quot;p&quot;&gt;{&lt;/span&gt;
        &lt;span class=&quot;k&quot;&gt;return&lt;/span&gt;
    &lt;span class=&quot;p&quot;&gt;}&lt;/span&gt;
    &lt;span class=&quot;n&quot;&gt;book&lt;/span&gt;&lt;span class=&quot;o&quot;&gt;.&lt;/span&gt;&lt;span class=&quot;nf&quot;&gt;setAuthor&lt;/span&gt;&lt;span class=&quot;p&quot;&gt;(&lt;/span&gt;&lt;span class=&quot;n&quot;&gt;author&lt;/span&gt;&lt;span class=&quot;p&quot;&gt;)&lt;/span&gt;
&lt;span class=&quot;p&quot;&gt;}&lt;/span&gt;
&lt;/code&gt;&lt;/pre&gt;&lt;/div&gt;
&lt;p&gt;Now, all the optionals can be checked at the beginning of your function and you can provide a code, that will be executed if the condition fails (inside the &lt;code&gt;else&lt;/code&gt; block).&lt;/p&gt;

&lt;p&gt;Actually if you forget to provide the code for when condition fails, compiler will throw an error! &lt;code&gt;Guard&lt;/code&gt; must always have an &lt;code&gt;else&lt;/code&gt; clause, that needs to contain &lt;code&gt;return&lt;/code&gt; or &lt;code&gt;break&lt;/code&gt; inside.&lt;/p&gt;

&lt;p&gt;This also allows you to name objects passed to your functions and to your closures in a sane way.&lt;/p&gt;

&lt;p&gt;I used to name function arguments and local variables differently – so I could clearly see which variables are of optional type and which ones are already unwrapped.&lt;/p&gt;

&lt;p&gt;In this case, instead of taking variables named &lt;code&gt;foo&lt;/code&gt; and &lt;code&gt;bar&lt;/code&gt; as function parameters, you could rewrite your code with &lt;code&gt;book&lt;/code&gt; and &lt;code&gt;author&lt;/code&gt;&lt;/p&gt;
&lt;div class=&quot;highlight&quot;&gt;&lt;pre&gt;&lt;code class=&quot;language-swift&quot; data-lang=&quot;swift&quot;&gt;&lt;span class=&quot;kd&quot;&gt;func&lt;/span&gt; &lt;span class=&quot;nf&quot;&gt;swiftGuardStyle2&lt;/span&gt;&lt;span class=&quot;p&quot;&gt;(&lt;/span&gt;&lt;span class=&quot;nv&quot;&gt;book&lt;/span&gt;&lt;span class=&quot;p&quot;&gt;:&lt;/span&gt; &lt;span class=&quot;kt&quot;&gt;Book&lt;/span&gt;&lt;span class=&quot;p&quot;&gt;?,&lt;/span&gt; &lt;span class=&quot;nv&quot;&gt;author&lt;/span&gt;&lt;span class=&quot;p&quot;&gt;:&lt;/span&gt; &lt;span class=&quot;kt&quot;&gt;Author&lt;/span&gt;&lt;span class=&quot;p&quot;&gt;?)&lt;/span&gt; &lt;span class=&quot;p&quot;&gt;{&lt;/span&gt;
    &lt;span class=&quot;k&quot;&gt;guard&lt;/span&gt; &lt;span class=&quot;k&quot;&gt;let&lt;/span&gt; &lt;span class=&quot;nv&quot;&gt;book&lt;/span&gt; &lt;span class=&quot;o&quot;&gt;=&lt;/span&gt; &lt;span class=&quot;n&quot;&gt;book&lt;/span&gt;&lt;span class=&quot;p&quot;&gt;,&lt;/span&gt; &lt;span class=&quot;n&quot;&gt;author&lt;/span&gt; &lt;span class=&quot;o&quot;&gt;=&lt;/span&gt; &lt;span class=&quot;n&quot;&gt;author&lt;/span&gt; &lt;span class=&quot;k&quot;&gt;else&lt;/span&gt; &lt;span class=&quot;p&quot;&gt;{&lt;/span&gt;
        &lt;span class=&quot;k&quot;&gt;return&lt;/span&gt;
    &lt;span class=&quot;p&quot;&gt;}&lt;/span&gt;
    &lt;span class=&quot;n&quot;&gt;book&lt;/span&gt;&lt;span class=&quot;o&quot;&gt;.&lt;/span&gt;&lt;span class=&quot;nf&quot;&gt;setAuthor&lt;/span&gt;&lt;span class=&quot;p&quot;&gt;(&lt;/span&gt;&lt;span class=&quot;n&quot;&gt;author&lt;/span&gt;&lt;span class=&quot;p&quot;&gt;)&lt;/span&gt;
&lt;span class=&quot;p&quot;&gt;}&lt;/span&gt;
&lt;/code&gt;&lt;/pre&gt;&lt;/div&gt;
&lt;p&gt;(this could have also been done in previous examples, but it feels much cleaner with &lt;code&gt;guard&lt;/code&gt;)&lt;/p&gt;

&lt;p&gt;You can also combine &lt;code&gt;guard&lt;/code&gt; with &lt;code&gt;where&lt;/code&gt;, to check specific condition on your optionals AND – you can use it to check conditions on non-optional values!&lt;br&gt;
(I found that not long ago on &lt;strong&gt;Eric Cerney&lt;/strong&gt;&amp;rsquo;s &lt;a href=&quot;http://ericcerney.com/swift-guard-statement/&quot;&gt;post&lt;/a&gt;)&lt;/p&gt;
&lt;div class=&quot;highlight&quot;&gt;&lt;pre&gt;&lt;code class=&quot;language-swift&quot; data-lang=&quot;swift&quot;&gt;&lt;span class=&quot;kd&quot;&gt;func&lt;/span&gt; &lt;span class=&quot;nf&quot;&gt;swiftGuardStyleWhere&lt;/span&gt;&lt;span class=&quot;p&quot;&gt;(&lt;/span&gt;&lt;span class=&quot;nv&quot;&gt;book&lt;/span&gt;&lt;span class=&quot;p&quot;&gt;:&lt;/span&gt; &lt;span class=&quot;kt&quot;&gt;Book&lt;/span&gt;&lt;span class=&quot;p&quot;&gt;?,&lt;/span&gt; &lt;span class=&quot;nv&quot;&gt;author&lt;/span&gt;&lt;span class=&quot;p&quot;&gt;:&lt;/span&gt; &lt;span class=&quot;kt&quot;&gt;Author&lt;/span&gt;&lt;span class=&quot;p&quot;&gt;?,&lt;/span&gt; &lt;span class=&quot;nv&quot;&gt;rating&lt;/span&gt;&lt;span class=&quot;p&quot;&gt;:&lt;/span&gt; &lt;span class=&quot;kt&quot;&gt;Int&lt;/span&gt;&lt;span class=&quot;p&quot;&gt;)&lt;/span&gt; &lt;span class=&quot;p&quot;&gt;{&lt;/span&gt;
    &lt;span class=&quot;k&quot;&gt;guard&lt;/span&gt; &lt;span class=&quot;n&quot;&gt;rating&lt;/span&gt; &lt;span class=&quot;o&quot;&gt;&amp;gt;&lt;/span&gt; &lt;span class=&quot;mi&quot;&gt;4&lt;/span&gt;&lt;span class=&quot;p&quot;&gt;,&lt;/span&gt; &lt;span class=&quot;k&quot;&gt;let&lt;/span&gt; &lt;span class=&quot;nv&quot;&gt;book&lt;/span&gt; &lt;span class=&quot;o&quot;&gt;=&lt;/span&gt; &lt;span class=&quot;n&quot;&gt;book&lt;/span&gt;&lt;span class=&quot;p&quot;&gt;,&lt;/span&gt; &lt;span class=&quot;n&quot;&gt;author&lt;/span&gt; &lt;span class=&quot;o&quot;&gt;=&lt;/span&gt; &lt;span class=&quot;n&quot;&gt;author&lt;/span&gt; &lt;span class=&quot;k&quot;&gt;where&lt;/span&gt; &lt;span class=&quot;n&quot;&gt;author&lt;/span&gt;&lt;span class=&quot;o&quot;&gt;.&lt;/span&gt;&lt;span class=&quot;n&quot;&gt;name&lt;/span&gt; &lt;span class=&quot;o&quot;&gt;==&lt;/span&gt; &lt;span class=&quot;s&quot;&gt;&quot;Bob&quot;&lt;/span&gt; &lt;span class=&quot;k&quot;&gt;else&lt;/span&gt; &lt;span class=&quot;p&quot;&gt;{&lt;/span&gt;
        &lt;span class=&quot;k&quot;&gt;return&lt;/span&gt;
    &lt;span class=&quot;p&quot;&gt;}&lt;/span&gt;
    &lt;span class=&quot;c1&quot;&gt;// will only execute if book and author are non nil&lt;/span&gt;
    &lt;span class=&quot;c1&quot;&gt;// and when author&#39;s name is &quot;Bob&quot;&lt;/span&gt;
    &lt;span class=&quot;c1&quot;&gt;// and when rating is &amp;gt; 4&lt;/span&gt;
    &lt;span class=&quot;n&quot;&gt;book&lt;/span&gt;&lt;span class=&quot;o&quot;&gt;.&lt;/span&gt;&lt;span class=&quot;nf&quot;&gt;setAuthor&lt;/span&gt;&lt;span class=&quot;p&quot;&gt;(&lt;/span&gt;&lt;span class=&quot;n&quot;&gt;author&lt;/span&gt;&lt;span class=&quot;p&quot;&gt;)&lt;/span&gt;
&lt;span class=&quot;p&quot;&gt;}&lt;/span&gt;
&lt;/code&gt;&lt;/pre&gt;&lt;/div&gt;
&lt;p&gt;With &lt;code&gt;guard&lt;/code&gt;, Swift programming becomes easier and your code becomes cleaner – you can now check for expected conditions, not for error case (like with &lt;code&gt;foo == nil&lt;/code&gt;) and as a bonus – you’re getting rid of that ugly indentation.&lt;/p&gt;

&lt;p&gt;You can find all code examples from the post on &lt;a href=&quot;https://gist.github.com/MariuszWisniewski/ef5744b6d39b87e0f32f&quot;&gt;GitHub&lt;/a&gt;.&lt;/p&gt;
</description>
        <pubDate>Sun, 24 Apr 2016 08:00:00 -0400</pubDate>
        <link>http://iosdev.nyc/blog/let-guard/</link>
        <guid isPermaLink="true">http://iosdev.nyc/blog/let-guard/</guid>
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