Add isnothing #29679

kescobo · 2018-10-16T21:25:00Z

This adds an isnothing() function to Base to mirror ismissing() and isnan() (see #29674)

I thought it would be pretty straightforward, but... I was naive.

First, I wasn't sure where to put it. Near notnothing() seemed like a good candidate, but I noticed that notnothing() is not exported. ismissing() is defined here near the definition of Missing

struct Missing end

"""
    missing
The singleton instance of type [`Missing`](@ref) representing a missing value.
"""
const missing = Missing()

"""
    ismissing(x)
Indicate whether `x` is [`missing`](@ref).
"""
ismissing(::Any) = false
ismissing(::Missing) = true

But Nothing seems to be defined in boot.jl, which doesn't seem like the best place for this function. Any advice on location from someone that knows the code better than me (eg. anyone at all) would be appreciated. And if it's not in boot.jl, where should I export it from? (I can't find where ismissing() is exported for example).

Second, folks on slack said that doing x === nothing was the most performant way to do this check, so I defined it as

isnothing(x::Any) = x === nothing ? true : false

But the way ismissing is defined above seems way more elegant. Should it be:

isnothing(::Any) = false
isnothing(::Nothing) = true

instead?

Finally, I'm having trouble building julia locally, so I can't do all the steps in CONTRIBUTING.md. I can't imagine how this could cause something to break, but I've been wrong with simple things before. Apologies if I'm missing something important.

JeffBezanson · 2018-10-16T21:28:55Z

x === nothing ? true : false is equivalent to just x === nothing, since === always returns a Bool. That said, I think the 2-method implementation ala ismissing is a bit better.

kescobo · 2018-10-16T21:32:04Z

Oh man, obviously 🤦‍♂️ . I feel like an idiot

ararslan · 2018-10-17T00:02:24Z

test/some.jl

+
+# isnothing()
+
+using Base: isnothing


I'd add this to base/exports.jl next to ismissing.

@ararslan check.

KristofferC · 2018-10-17T14:28:56Z

base/some.jl

@@ -40,6 +40,15 @@ Throw an error if `x === nothing`, and return `x` if not.
 notnothing(x::Any) = x
 notnothing(::Nothing) = throw(ArgumentError("nothing passed to notnothing"))

+"""


Needs to be added to the documentation so it shows up.

Done - I added it next to Nothing.

kescobo · 2018-10-17T16:11:44Z

@KristofferC Should I be the one to add to NEWS.md?

KristofferC · 2018-10-17T16:13:01Z

It would be good :) But if not, the label is here to make sure we do it before the release.

kescobo · 2018-10-17T19:08:50Z

Check.

kescobo · 2018-10-17T19:10:19Z

One last (hopefully) question: should I be the one to squash (to comply with point 2 here) or will that be done when merging?

fredrikekre · 2018-10-17T19:36:02Z

Can be done on merge.

JeffBezanson · 2018-10-17T19:52:42Z

Neither of the items under "New language features" currently in NEWS are new language features, but that can be edited separately.

kescobo · 2018-10-17T21:31:05Z

Heh - I didn't think so either, but the NEWS.md is pretty sparse, and that seemed more appropriate than any of the other headers ¯_(ツ)_/¯

changes between Julia 1.0 and 1.1, including: - Custom .css-style for compat admonitions. - Information about compat annotations to CONTRIBUTING.md. - NEWS.md entry for PRs #30090, #30035, #30022, #29978, #29969, #29858, #29845, #29754, #29638, #29636, #29615, #29600, #29506, #29469, #29316, #29259, #29178, #29153, #29033, #28902, #28761, #28745, #28708, #28696, #29997, #28790, #29092, #29108, #29782 - Compat annotation for PRs #30090, #30013, #29978, #29890, #29858, #29827, #29754, #29679, #29636, #29623, #29600, #29440, #29316, #29259, #29178, #29157, #29153, #29033, #28902, #28878, #28761, #28708, #28156, #29733, #29670, #29997, #28790, #29092, #29108, #29782, #25278 - Documentation for broadcasting CartesianIndices (#30230). - Documentation for Base.julia_cmd(). - Documentation for colon constructor of CartesianIndices (#29440). - Documentation for ^(::Matrix, ::Number) and ^(::Number, ::Matrix). - Run NEWS-update.jl. Co-authored-by: Morten Piibeleht <[email protected]> Co-authored-by: Fredrik Ekre <[email protected]>

Addition of NEWS and compat admonitions for important changes between Julia 1.0 and 1.1, including: - Custom .css-style for compat admonitions. - Information about compat annotations to CONTRIBUTING.md. - NEWS.md entry for PRs #30090, #30035, #30022, #29978, #29969, #29858, #29845, #29754, #29638, #29636, #29615, #29600, #29506, #29469, #29316, #29259, #29178, #29153, #29033, #28902, #28761, #28745, #28708, #28696, #29997, #28790, #29092, #29108, #29782 - Compat annotation for PRs #30090, #30013, #29978, #29890, #29858, #29827, #29754, #29679, #29636, #29623, #29600, #29440, #29316, #29259, #29178, #29157, #29153, #29033, #28902, #28878, #28761, #28708, #28156, #29733, #29670, #29997, #28790, #29092, #29108, #29782, #25278 - Documentation for broadcasting CartesianIndices (#30230). - Documentation for Base.julia_cmd(). - Documentation for colon constructor of CartesianIndices (#29440). - Documentation for ^(::Matrix, ::Number) and ^(::Number, ::Matrix). - Run NEWS-update.jl. Co-authored-by: Morten Piibeleht <[email protected]> Co-authored-by: Fredrik Ekre <[email protected]>

kescobo added 2 commits October 16, 2018 16:41

Add isnothing() function

4990881

add tests

710ff6c

Switch to two method version

d17bd7e

ararslan reviewed Oct 17, 2018

View reviewed changes

Export function

edc7cf5

KristofferC approved these changes Oct 17, 2018

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KristofferC reviewed Oct 17, 2018

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KristofferC added the needs news A NEWS entry is required for this change label Oct 17, 2018

Add docstring to doc/src/base.md

6a5e438

Add to NEWS.md

c1ee8fa

KristofferC approved these changes Oct 17, 2018

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JeffBezanson approved these changes Oct 17, 2018

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fredrikekre removed the needs news A NEWS entry is required for this change label Oct 17, 2018

JeffBezanson merged commit d401033 into JuliaLang:master Oct 18, 2018

kescobo mentioned this pull request Oct 20, 2018

Add isnothing() function? #29674

Closed

fredrikekre added a commit that referenced this pull request Nov 30, 2018

Compat annotation for #29679 (isnothing).

dae7a0d

fredrikekre added a commit that referenced this pull request Nov 30, 2018

Compat annotation for #29679 (isnothing).

19de222

fredrikekre added a commit that referenced this pull request Dec 1, 2018

Compat annotation for #29679 (isnothing).

a2321a3

fredrikekre added a commit that referenced this pull request Dec 1, 2018

Compat annotation for #29679 (isnothing).

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fredrikekre added a commit that referenced this pull request Dec 3, 2018

Compat annotation for #29679 (isnothing).

9125877

fredrikekre added a commit that referenced this pull request Dec 4, 2018

Compat annotation for #29679 (isnothing).

05a4dfd

fredrikekre added a commit that referenced this pull request Dec 4, 2018

Compat annotation for #29679 (isnothing).

75acf18

odow mentioned this pull request Jan 1, 2019

✅ Fix JuMPExtension print tests jump-dev/JuMP.jl#1713

Merged

galenlynch mentioned this pull request Jan 6, 2019

Add skipnothing function which returns an iterator without nothing #30549

Closed

ali-ramadhan mentioned this pull request Oct 23, 2019

More coriolis options CliMA/Oceananigans.jl#438

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Add isnothing #29679

Add isnothing #29679

kescobo commented Oct 16, 2018

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Add isnothing #29679

Add isnothing #29679

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