Add ToString singleton op on Ints

Author: MaximeKjaer

compiler/src/dotty/tools/dotc/core/Definitions.scala

@@ -905,7 +905,7 @@ class Definitions {
         tpnme.Equals, tpnme.NotEquals,
         tpnme.Plus, tpnme.Minus, tpnme.Times, tpnme.Div, tpnme.Mod,
         tpnme.Lt, tpnme.Gt, tpnme.Ge, tpnme.Le,
-        tpnme.Abs, tpnme.Negate, tpnme.Min, tpnme.Max,
+        tpnme.Abs, tpnme.Negate, tpnme.Min, tpnme.Max, tpnme.ToString,
         tpnme.Not, tpnme.Xor, tpnme.And, tpnme.Or
       ).contains(sym.name)
 

compiler/src/dotty/tools/dotc/core/StdNames.scala

@@ -226,6 +226,7 @@ object StdNames {
     final val Plus: N      = "+"
     final val S: N         = "S"
     final val Times: N     = "*"
+    final val ToString: N  = "ToString"
     final val Xor: N       = "^"
 
     final val ClassfileAnnotation: N = "ClassfileAnnotation"

compiler/src/dotty/tools/dotc/core/Types.scala

@@ -3636,6 +3636,7 @@ object Types {
             case tpnme.Abs => constantFold1(intValue, _.abs)
             case tpnme.Negate => constantFold1(intValue, x => -x)
             case tpnme.Not => constantFold1(boolValue, x => !x)
+            case tpnme.ToString => constantFold1(intValue, _.toString)
             case _ => None
           } else if (args.length == 2) tycon.symbol.name match {
             case tpnme.Equals => constantFold2(constValue, _ == _)

library/src/scala/compiletime/ops/package.scala

@@ -21,6 +21,7 @@ package object ops {
   type Negate[X <: Int] <: Int
   type Min[X <: Int, Y <: Int] <: Int
   type Max[X <: Int, Y <: Int] <: Int
+  type ToString[X <: Int] <: String
 
   type ![X <: Boolean] <: Boolean
   @infix type ^[X <: Boolean, Y <: Boolean] <: Boolean

tests/neg/singleton-ops.scala

@@ -92,4 +92,9 @@ object Test {
   val t65: ![false] = true
   val t66: ![true] = true // error
   val t67: ![false] = false // error
+
+  val t68: ToString[213] = "213"
+  val t69: ToString[-1] = "-1"
+  val t70: ToString[0] = "-0" // error
+  val t71: ToString[200] = "100" // error
 }