Conditional modifications

README.md

@@ -31,6 +31,13 @@ person
   .modify(_.age).using(_ - 1)
 ````
 
+**Modify conditionally:**
+
+````scala
+person.modify(_.address.street.name).setToIfDefined(Some("3 00 Ln."))
+person.modify(_.address.street.name).setToIf(shouldChangeAddress)("3 00 Ln.")
+````
+
 **Modify several fields in one go:**
 
 ````scala
@@ -183,7 +190,7 @@ Read [the blog](http://www.warski.org/blog/2015/02/quicklens-modify-deeply-neste
 Available in Maven Central:
 
 ````scala
-val quicklens = "com.softwaremill.quicklens" %% "quicklens" % "1.4.7"
+val quicklens = "com.softwaremill.quicklens" %% "quicklens" % "1.4.8"
 ````
 
 Also available for [Scala.js](http://www.scala-js.org)!

project/Build.scala

@@ -6,7 +6,7 @@ import sbt._
 object BuildSettings {
   val buildSettings = Defaults.coreDefaultSettings ++ Seq (
     organization  := "com.softwaremill.quicklens",
-    version       := "1.4.7",
+    version       := "1.4.8",
     scalaVersion  := "2.11.8",
     crossScalaVersions := Seq("2.11.8", "2.12.0-RC1"),
     // Sonatype OSS deployment

quicklens/src/main/scala/com/softwaremill/quicklens/package.scala

@@ -56,11 +56,30 @@ package object quicklens {
      * @return A copy of the root object with the (deeply nested) field(s) modified.
      */
     def using(mod: U => U): T = doModify(obj, mod)
+    /**
+      * Transform the value of the field(s) using the given function, if the condition is true. Otherwise, returns the
+      * original object unchanged.
+      * @return A copy of the root object with the (deeply nested) field(s) modified, if `condition` is true.
+      */
+    def usingIf(condition: Boolean)(mod: U => U): T = if (condition) doModify(obj, mod) else obj
     /**
      * Set the value of the field(s) to a new value.
      * @return A copy of the root object with the (deeply nested) field(s) set to the new value.
      */
     def setTo(v: U): T = doModify(obj, _ => v)
+    /**
+      * Set the value of the field(s) to a new value, if it is defined. Otherwise, returns the original object
+      * unchanged.
+      * @return A copy of the root object with the (deeply nested) field(s) set to the new value, if it is defined.
+      */
+    def setToIfDefined(v: Option[U]): T = v.fold(obj)(setTo)
+    /**
+      * Set the value of the field(s) to a new value, if the condition is true. Otherwise, returns the original object
+      * unchanged.
+      * @return A copy of the root object with the (deeply nested) field(s) set to the new value, if `condition` is
+      *         true.
+      */
+    def setToIf(condition: Boolean)(v: => U): T = if (condition) setTo(v) else obj
   }
 
   implicit class AbstractPathModifyPimp[T, U](f1: T => PathModify[T, U]) {

tests/src/test/scala/com/softwaremill/quicklens/ModifySimpleTest.scala

@@ -15,4 +15,12 @@ class ModifySimpleTest extends FlatSpec with Matchers {
   it should "modify several fields" in {
     modifyAll(b1)(_.b2, _.b3.each).using(duplicate) should be (b1dupdup)
   }
+
+  it should "modify a case class field if the condition is true" in {
+    modify(a5)(_.name).usingIf(true)(duplicate) should be (a5dup)
+  }
+
+  it should "leave a case class unchanged if the condition is flase" in {
+    modify(a5)(_.name).usingIf(false)(duplicate) should be (a5)
+  }
 }

tests/src/test/scala/com/softwaremill/quicklens/SetToSimpleTest.scala

@@ -7,4 +7,20 @@ class SetToSimpleTest extends FlatSpec with Matchers {
   it should "set a new value of a single-nested case class field" in {
     modify(a1)(_.a2.a3.a4.a5.name).setTo("mod") should be (a1mod)
   }
+
+  it should "set a new value in a case class if the condition is true" in {
+    modify(a1)(_.a2.a3.a4.a5.name).setToIf(true)("mod") should be (a1mod)
+  }
+
+  it should "leave a case class unchanged if the condition is false" in {
+    modify(a1)(_.a2.a3.a4.a5.name).setToIf(false)("mod") should be (a1)
+  }
+
+  it should "set a new value in a case class if it is defined" in {
+    modify(a1)(_.a2.a3.a4.a5.name).setToIfDefined(Some("mod")) should be (a1mod)
+  }
+
+  it should "leave a case class unchanged if the value is not defined" in {
+    modify(a1)(_.a2.a3.a4.a5.name).setToIfDefined(None) should be (a1)
+  }
 }