Merge pull request #11668 from dotty-staging/add-conversion-into

Add Conversion.into method

Author: odersky

language-server/test/dotty/tools/languageserver/CompletionTest.scala

@@ -30,7 +30,7 @@ class CompletionTest {
 
   @Test def completionFromScalaPackage: Unit = {
     code"class Foo { val foo: Conv${m1} }".withSource
-      .completion(m1, Set(("Conversion", Class, "scala.Conversion")))
+      .completion(m1, Set(("Conversion", Class, "class and object Conversion")))
   }
 
   @Test def completionFromScalaPackageObject: Unit = {

library/src/scala/Conversion.scala

@@ -17,7 +17,16 @@ package scala
 *  Also note that in bootstrapped dotty, `Predef.<:<` should inherit from
 *  `Conversion`. This would cut the number of special cases in `discardForView`
 *  from two to one.
+*
+*  The `Conversion` class can also be used to convert explicitly, using
+*  the `convert` extension method.
 */
 @java.lang.FunctionalInterface
 abstract class Conversion[-T, +U] extends Function1[T, U]:
+  /** Convert value `x` of type `T` to type `U` */
   def apply(x: T): U
+object Conversion:
+
+  extension [T](x: T)
+    /** `x.convert[U]` converts a value `x` of type `T` to type `U` */
+    def convert[U](using c: Conversion[T, U]) = c(x)

tests/pos/convert.scala

@@ -0,0 +1,7 @@
+import Conversion.convert
+
+given Conversion[String, Int] = _.length
+given Conversion[Int, String] = _.toString
+
+def f(x: String): Int = x.convert
+def g(x: Int): String = x.convert[String]