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betterFors don't drop the trailing map if it would result i…
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54 changes: 54 additions & 0 deletions
54
compiler/src/dotty/tools/dotc/transform/localopt/DropForMap.scala
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| Original file line number | Diff line number | Diff line change |
|---|---|---|
| @@ -0,0 +1,54 @@ | ||
| package dotty.tools.dotc | ||
| package transform.localopt | ||
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| import dotty.tools.dotc.ast.tpd.* | ||
| import dotty.tools.dotc.core.Decorators.* | ||
| import dotty.tools.dotc.core.Contexts.* | ||
| import dotty.tools.dotc.core.StdNames.* | ||
| import dotty.tools.dotc.core.Symbols.* | ||
| import dotty.tools.dotc.core.Types.* | ||
| import dotty.tools.dotc.transform.MegaPhase.MiniPhase | ||
| import dotty.tools.dotc.ast.desugar | ||
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| /** Drop unused trailing map calls in for comprehensions. | ||
| * We can drop the map call if: | ||
| * - it won't change the type of the expression, and | ||
| * - the function is an identity function or a const function to unit. | ||
| * | ||
| * The latter condition is checked in [[Desugar.scala#makeFor]] | ||
| */ | ||
| class DropForMap extends MiniPhase: | ||
| import DropForMap.* | ||
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| override def phaseName: String = DropForMap.name | ||
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| override def description: String = DropForMap.description | ||
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| override def transformApply(tree: Apply)(using Context): Tree = | ||
| if !tree.hasAttachment(desugar.TrailingForMap) then tree | ||
| else tree match | ||
| case aply @ Apply(MapCall(f), List(Lambda(List(param), body))) | ||
| if f.tpe =:= aply.tpe => // make sure that the type of the expression won't change | ||
| f // drop the map call | ||
| case _ => | ||
| tree.removeAttachment(desugar.TrailingForMap) | ||
| tree | ||
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| private object Lambda: | ||
| def unapply(tree: Tree)(using Context): Option[(List[ValDef], Tree)] = | ||
| tree match | ||
| case Block(List(defdef: DefDef), Closure(Nil, ref, _)) | ||
| if ref.symbol == defdef.symbol && !defdef.paramss.exists(_.forall(_.isType)) => | ||
| Some((defdef.termParamss.flatten, defdef.rhs)) | ||
| case _ => None | ||
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| private object MapCall: | ||
| def unapply(tree: Tree)(using Context): Option[Tree] = tree match | ||
| case Select(f, nme.map) => Some(f) | ||
| case Apply(fn, _) => unapply(fn) | ||
| case TypeApply(fn, _) => unapply(fn) | ||
| case _ => None | ||
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| object DropForMap: | ||
| val name: String = "dropForMap" | ||
| val description: String = "Drop unused trailing map calls in for comprehensions" |
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| Original file line number | Diff line number | Diff line change |
|---|---|---|
| @@ -0,0 +1,13 @@ | ||
| import scala.language.experimental.betterFors | ||
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| case class Container[A](val value: A) { | ||
| def map[B](f: A => B): Container[B] = Container(f(value)) | ||
| } | ||
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| sealed trait Animal | ||
| case class Dog() extends Animal | ||
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| def opOnDog(dog: Container[Dog]): Container[Animal] = | ||
| for | ||
| v <- dog | ||
| yield v |
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| Original file line number | Diff line number | Diff line change |
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| @@ -0,0 +1,4 @@ | ||
| MySome(()) | ||
| MySome(2) | ||
| MySome((2,3)) | ||
| MySome((2,(3,4))) |
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| Original file line number | Diff line number | Diff line change |
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| @@ -0,0 +1,64 @@ | ||
| import scala.language.experimental.betterFors | ||
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| class myOptionModule(doOnMap: => Unit) { | ||
| sealed trait MyOption[+A] { | ||
| def map[B](f: A => B): MyOption[B] = this match { | ||
| case MySome(x) => { | ||
| doOnMap | ||
| MySome(f(x)) | ||
| } | ||
| case MyNone => MyNone | ||
| } | ||
| def flatMap[B](f: A => MyOption[B]): MyOption[B] = this match { | ||
| case MySome(x) => f(x) | ||
| case MyNone => MyNone | ||
| } | ||
| } | ||
| case class MySome[A](x: A) extends MyOption[A] | ||
| case object MyNone extends MyOption[Nothing] | ||
| object MyOption { | ||
| def apply[A](x: A): MyOption[A] = MySome(x) | ||
| } | ||
| } | ||
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| object Test extends App { | ||
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| val myOption = new myOptionModule(println("map called")) | ||
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| import myOption.* | ||
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| def portablePrintMyOption(opt: MyOption[Any]): Unit = | ||
| if opt == MySome(()) then | ||
| println("MySome(())") | ||
| else | ||
| println(opt) | ||
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| val z = for { | ||
| a <- MyOption(1) | ||
| b <- MyOption(()) | ||
| } yield () | ||
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| portablePrintMyOption(z) | ||
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| val z2 = for { | ||
| a <- MyOption(1) | ||
| b <- MyOption(2) | ||
| } yield b | ||
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| portablePrintMyOption(z2) | ||
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| val z3 = for { | ||
| a <- MyOption(1) | ||
| (b, c) <- MyOption((2, 3)) | ||
| } yield (b, c) | ||
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| portablePrintMyOption(z3) | ||
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| val z4 = for { | ||
| a <- MyOption(1) | ||
| (b, (c, d)) <- MyOption((2, (3, 4))) | ||
| } yield (b, (c, d)) | ||
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| portablePrintMyOption(z4) | ||
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| } |