Improvements to implicits #1918
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| Original file line number | Diff line number | Diff line change |
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| @@ -0,0 +1,30 @@ | ||
| package generic | ||
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| import Shapes._ | ||
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| /** enum Color { | ||
| * case Red | ||
| * case Green | ||
| * case Blue | ||
| * } | ||
| */ | ||
| sealed trait Color extends Enum | ||
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| object Color extends EnumValues[Color](3) { | ||
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| private def $new(tag: Int, name: String) = new Color { | ||
| def enumTag = tag | ||
| override def toString = name | ||
| registerEnumValue(this) | ||
| } | ||
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There was a problem hiding this comment. Can we have a named subclass of |
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| val Red: Color = $new(0, "Red") | ||
| val Green: Color = $new(1, "Green") | ||
| val Blue: Color = $new(2, "Blue") | ||
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| implicit val ColorShape: Color `shaped` EnumValue[Color] = | ||
| new (Color `shaped` EnumValue[Color]) { | ||
| def toShape(x: Color) = EnumValue(x.enumTag) | ||
| def fromShape(x: EnumValue[Color]) = Color.value(x.tag) | ||
| } | ||
| } | ||
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| Original file line number | Diff line number | Diff line change |
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| @@ -0,0 +1,18 @@ | ||
| package generic | ||
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| import Shapes.Singleton | ||
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| trait Enum { | ||
| def enumTag: Int | ||
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There was a problem hiding this comment. What use cases do you envision for |
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| } | ||
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| trait FiniteEnum extends Enum | ||
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| abstract class EnumValues[E <: Enum](numVals: Int) { | ||
| private var myValues = new Array[AnyRef](numVals) | ||
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| def registerEnumValue(v: E) = | ||
| myValues(v.enumTag) = v | ||
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There was a problem hiding this comment. Can we somehow restrict the visibility of this method? |
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| def value: IndexedSeq[E] = (myValues: IndexedSeq[AnyRef]).asInstanceOf[IndexedSeq[E]] | ||
| } | ||
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| Original file line number | Diff line number | Diff line change |
|---|---|---|
| @@ -0,0 +1,89 @@ | ||
| package generic | ||
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| import Shapes._ | ||
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| /** enum List[T] { | ||
| * case Cons(x: T, xs: List[T]) | ||
| * case Nil() | ||
| * } | ||
| */ | ||
| sealed trait List0[T] extends Enum | ||
| object List0 { | ||
| abstract case class Cons[T](hd: T, tl: List0[T]) extends List0[T] { | ||
| def enumTag = 0 | ||
| } | ||
| object Cons { | ||
| def apply[T](x: T, xs: List0[T]): List0[T] = new Cons(x, xs) {} | ||
| implicit def ConsShape[T]: Cons[T] `shaped` Prod[T, List0[T]] = | ||
| new (Cons[T] `shaped` Prod[T, List0[T]]) { | ||
| def toShape(x: Cons[T]) = Prod(x.hd, x.tl) | ||
| def fromShape(p: Prod[T, List0[T]]) = new Cons(p.fst, p.snd) {} | ||
| } | ||
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There was a problem hiding this comment. @odersky Am I right in thinking that you'd like the There was a problem hiding this comment. And, in general, which parts of the There was a problem hiding this comment. @xeno-by The |
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| } | ||
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| abstract case class Nil[T]() extends List0[T] { | ||
| def enumTag = 1 | ||
| } | ||
| object Nil { | ||
| def apply[T](): List0[T] = new Nil[T]() {} | ||
| implicit def NilShape[T]: Nil[T] `shaped` Unit = | ||
| new (Nil[T] `shaped` Unit) { | ||
| def toShape(x: Nil[T]) = () | ||
| def fromShape(x: Unit) = new Nil[T]() {} | ||
| } | ||
| } | ||
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| implicit def List0Shape[T]: List0[T] `shaped` Sum[Cons[T], Nil[T]] = | ||
| new (List0[T] `shaped` Sum[Cons[T], Nil[T]]) { | ||
| def toShape(x: List0[T]) = x match { | ||
| case x: Cons[T] => Fst(x) | ||
| case x: Nil[T] => Snd(x) | ||
| } | ||
| def fromShape(x: Sum[Cons[T], Nil[T]]) = x match { | ||
| case Fst(c) => c | ||
| case Snd(n) => n | ||
| } | ||
| } | ||
| } | ||
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| /** enum List[T] { | ||
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There was a problem hiding this comment. Is the variance modifier omitted here on purpose? There was a problem hiding this comment. There are actually two sources, one without variance for List0, the other with variance for List1. |
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| * case Cons(x: T, xs: List[T]) | ||
| * case Nil extends List[Nothing] | ||
| * } | ||
| */ | ||
| sealed trait List[+T] extends Enum | ||
| object List { | ||
| abstract case class Cons[T](hd: T, tl: List[T]) extends List[T] { | ||
| def enumTag = 0 | ||
| } | ||
| object Cons { | ||
| def apply[T](x: T, xs: List[T]): List[T] = new Cons(x, xs) {} | ||
| type Shape[T] = Prod[T, List[T]] | ||
| implicit def ConsShape[T]: Cons[T] `shaped` Shape[T] = | ||
| new (Cons[T] `shaped` Shape[T]) { | ||
| def toShape(x: Cons[T]) = Prod(x.hd, x.tl) | ||
| def fromShape(p: Shape[T]) = new Cons(p.fst, p.snd) {} | ||
| } | ||
| } | ||
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| val Nil = new List[Nothing] { | ||
| def enumTag = 1 | ||
| override def toString = "Nil" | ||
| } | ||
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| implicit def NilSingleton: Singleton[Nil.type] = new Singleton[Nil.type](Nil) | ||
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| type Shape[T] = Sum[Cons[T], Nil.type] | ||
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| implicit def ListShape[T]: List[T] `unfolds` Shape[T] = | ||
| new (List[T] `shaped` Shape[T]) { | ||
| def toShape(x: List[T]) = x match { | ||
| case x: Cons[T] => Fst(x) | ||
| case Nil => Snd(Nil) | ||
| } | ||
| def fromShape(x: Shape[T]): List[T] = x match { | ||
| case Fst(c) => c | ||
| case Snd(n) => n | ||
| } | ||
| } | ||
| } | ||
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Why was this prohibited in scalac?