diff options
| -rw-r--r-- | src/library/scala/Function.scala | 29 |
1 files changed, 28 insertions, 1 deletions
diff --git a/src/library/scala/Function.scala b/src/library/scala/Function.scala index 95d3aba859..9cdaf90349 100644 --- a/src/library/scala/Function.scala +++ b/src/library/scala/Function.scala @@ -11,12 +11,39 @@ package scala +import annotation.experimental + /** A module defining utility methods for higher-order functional programming. * * @author Martin Odersky * @version 1.0, 29/11/2006 */ -object Function { +object Function +{ + /** Given a starting value, the returned object can be repeatedly + * applied with Function1s and then the result retrieved with apply(). + * At each iteration the argument is checked for null before function + * application; if it is ever null, the result will be null. + * + * <pre> + * case class Bop(next: Bop) + * val x = Bop(Bop(Bop(null))) + * ?:(x)(_.next)() // returns Bop(Bop(null)) + * ?:(x)(_.next)(_.next)() // returns Bop(null) + * ?:(x)(_.next)(_.next)(_.next)() // returns null + * ?:(x)(_.next)(_.next)(_.next)(_.next)() // still returns null! + * </pre> + * + * @param x The starting value + * @return The ?: object, containing apply methods T => U and () => T + */ + @experimental + case class ?:[T](x: T) { + def apply(): T = x + def apply[U >: Null](f: T => U): ?:[U] = + if (x == null) ?:[U](null) + else ?:[U](f(x)) + } /** Given a sequence of functions <code>f<sub>1</sub></code>, ..., * <code>f<sub>n</sub></code>, return the function <code>f<sub>1</sub> |