Merge pull request #14431 from dotty-staging/scala-compiletime-ops-string-charat

Add compiletime.ops.string.CharAt

Author: mbovel

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

@@ -1167,7 +1167,7 @@ class Definitions {
   )
   private val compiletimePackageBooleanTypes: Set[Name] = Set(tpnme.Not, tpnme.Xor, tpnme.And, tpnme.Or)
   private val compiletimePackageStringTypes: Set[Name] = Set(
-    tpnme.Plus, tpnme.Length, tpnme.Substring, tpnme.Matches
+    tpnme.Plus, tpnme.Length, tpnme.Substring, tpnme.Matches, tpnme.CharAt
   )
   private val compiletimePackageOpTypes: Set[Name] =
     Set(tpnme.S)

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

@@ -234,6 +234,7 @@ object StdNames {
     final val Plus: N                 = "+"
     final val S: N                    = "S"
     final val Substring: N            = "Substring"
+    final val CharAt: N               = "CharAt"
     final val Times: N                = "*"
     final val ToInt: N                = "ToInt"
     final val ToLong: N               = "ToLong"

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

@@ -4456,6 +4456,8 @@ object Types {
               case tpnme.Matches    => constantFold2(stringValue, _ matches _)
               case tpnme.Substring  =>
                 constantFold3(stringValue, intValue, intValue, (s, b, e) => s.substring(b, e))
+              case tpnme.CharAt     =>
+                constantFold2AB(stringValue, intValue, _ charAt _)
               case _ => None
             } else if (owner == defn.CompiletimeOpsBooleanModuleClass) name match {
               case tpnme.Not        => constantFold1(boolValue, x => !x)

library/src/scala/compiletime/ops/any.scala

@@ -1,8 +1,6 @@
 package scala.compiletime
 package ops
 
-import annotation.experimental
-
 object any:
   /** Equality comparison of two singleton types.
    * ```scala
@@ -41,7 +39,6 @@ object any:
    * ```
    * @syntax markdown
    */
-  @experimental
   type IsConst[X] <: Boolean
 
   /** String conversion of a constant singleton type.
@@ -51,5 +48,4 @@ object any:
    *  ```
    *  @syntax markdown
    */
-  @experimental
   type ToString[+X] <: String

library/src/scala/compiletime/ops/double.scala

@@ -1,9 +1,6 @@
 package scala.compiletime
 package ops
 
-import scala.annotation.experimental
-
-@experimental
 object double:
   /** Addition of two `Double` singleton types.
    *  ```scala

library/src/scala/compiletime/ops/float.scala

@@ -1,9 +1,6 @@
 package scala.compiletime
 package ops
 
-import scala.annotation.experimental
-
-@experimental
 object float:
   /** Addition of two `Float` singleton types.
    *  ```scala

library/src/scala/compiletime/ops/int.scala

@@ -1,8 +1,6 @@
 package scala.compiletime
 package ops
 
-import annotation.experimental
-
 object int:
   /** Successor of a natural number where zero is the type 0 and successors are reduced as if the definition was:
    *
@@ -192,7 +190,6 @@ object int:
    *  ```
    *  @syntax markdown
    */
-  @experimental
   type ToLong[+X <: Int] <: Long
 
   /** Float conversion of an `Int` singleton type.
@@ -201,7 +198,6 @@ object int:
    *  ```
    *  @syntax markdown
    */
-  @experimental
   type ToFloat[+X <: Int] <: Float
 
   /** Double conversion of an `Int` singleton type.
@@ -210,7 +206,6 @@ object int:
    *  ```
    *  @syntax markdown
    */
-  @experimental
   type ToDouble[+X <: Int] <: Double
 
   /** Number of zero bits preceding the highest-order ("leftmost")
@@ -225,5 +220,4 @@ object int:
    *  ```
    *  @syntax markdown
    */
-  @experimental
   type NumberOfLeadingZeros[+X <: Int] <: Int

library/src/scala/compiletime/ops/long.scala

@@ -1,9 +1,6 @@
 package scala.compiletime
 package ops
 
-import scala.annotation.experimental
-
-@experimental
 object long:
   /** Successor of a natural number where zero is the type 0 and successors are reduced as if the definition was:
    *

library/src/scala/compiletime/ops/string.scala

@@ -1,8 +1,6 @@
 package scala.compiletime
 package ops
 
-import scala.annotation.experimental
-
 object string:
   /** Concatenation of two `String` singleton types.
    *  ```scala
@@ -18,7 +16,6 @@ object string:
    *  ```
    *  @syntax markdown
    */
-  @experimental
   type Length[+X <: String] <: Int
 
   /** Substring of a `String` singleton type, with a singleton type
@@ -31,7 +28,6 @@ object string:
    *  ```
    *  @syntax markdown
    */
-  @experimental
   type Substring[+S <: String, +IBeg <: Int, +IEnd <: Int] <: String
 
   /** Tests if this `String` singleton type matches the given
@@ -41,5 +37,14 @@ object string:
    *  ```
    *  @syntax markdown
    */
-  @experimental
   type Matches[+S <: String, +Regex <: String] <: Boolean
+
+  /** Returns the Char type at the specified index.
+   *  An index ranges from 0 to Length[S] - 1. The first Char of
+   *  the sequence is at index 0, the next at index 1, and so on.
+   *  ```scala
+   *  val c: CharAt["hello", 0] = 'h'
+   *  ```
+   *  @syntax markdown
+   */
+  type CharAt[+S <: String, +Idx <: Int] <: Char

tests/neg/singleton-ops-string.scala

@@ -15,4 +15,23 @@ object Test {
 
   val t9: Matches["hamburger", "ham.*"] = true
   val t10: Matches["hamburger", "ham.*"] = false // error
+
+  val t11: CharAt["String", 0] = 'S'
+  val t12: CharAt["String", 1] = 't'
+  val t13: CharAt["String", 2] = '!' // error
+  //                             ^^^
+  //                             Found:    ('!' : Char)
+  //                             Required: ('r' : Char)
+  val t14: CharAt["String", 3] = '!' // error
+  //                             ^^^
+  //                             Found:    ('!' : Char)
+  //                             Required: ('i' : Char)
+  val t15: CharAt["String", 4] = 'n'
+  val t16: CharAt["String", 5] = 'g'
+  val t17: CharAt["String", 6]  = '!' // error
+  //       ^
+  //       String index out of range: 6
+  val t18: CharAt["String", -1] = '?' // error
+  //       ^
+  //       String index out of range: -1
 }