diff options
Diffstat (limited to 'src/library/scala/Predef.scala')
| -rw-r--r-- | src/library/scala/Predef.scala | 14 |
1 files changed, 12 insertions, 2 deletions
diff --git a/src/library/scala/Predef.scala b/src/library/scala/Predef.scala index 565aa363e8..aa718e1892 100644 --- a/src/library/scala/Predef.scala +++ b/src/library/scala/Predef.scala @@ -76,6 +76,10 @@ object Predef { val Map = collection.immutable.Map val Set = collection.immutable.Set + // no longer a view: subsumed by `conforms` (which is less likely to give rise to ambiguities) + // @see `conforms` for the implicit version + def identity[A](x: A): A = x + // errors and asserts ------------------------------------------------- def error(message: String): Nothing = throw new RuntimeException(message) @@ -180,8 +184,6 @@ object Predef { // views -------------------------------------------------------------- - implicit def identity[A](x: A): A = x - implicit def byteWrapper(x: Byte) = new runtime.RichByte(x) implicit def shortWrapper(x: Short) = new runtime.RichShort(x) implicit def intWrapper(x: Int) = new runtime.RichInt(x) @@ -249,5 +251,13 @@ object Predef { override def toString: String = xs.mkString("") } + // used, for example, in the encoding of generalized constraints + // we need a new type constructor `<:<` and evidence `conforms`, as + // reusing `Function2` and `identity` leads to ambiguities (any2stringadd is inferred) + // to constrain any abstract type T that's in scope in a method's argument list (not just the method's own type parameters) + // simply add an implicit argument of type `T <:< U`, where U is the required upper bound (for lower-bounds, use: `U <: T`) + sealed abstract class <:<[-From, +To] extends (From => To) + implicit def conforms[A]: A <:< A = new (A <:< A) {def apply(x: A) = x} + def currentThread = java.lang.Thread.currentThread() } |