Imported From: https://issues.scala-lang.org/browse/SI-5267?orig=1
Reporter: @retronym

@paulp said:
bb23d766bc

@ijuma said:
Yay! :)

Marcin Kielar (zorba128) said:
Hi

Just wanted to ask what is the status of partial Function1 specialization - this ticket seems closed/resolved, while Function1 in scala 2.11.2 doesn't seem to be AnyRef specialized...

regards,
Marcin

@retronym said (edited on Oct 10, 2014 7:46:54 AM UTC):
Unfortunately AnyRef specialization had to be removed from Functions in scala/scala@cc3badae17e. Discussion of the problems it caused is here: https://groups.google.com/d/msg/scala-internals/5P5TS9ZWe_w/39S8q1WJYF8J.

We don't have plans to revisit this in forseeable future.

What we do have, however, is experimental support for SAMs in Scala 2.11.

scala> trait IntFunction[A] { def apply(i: A): Int }
defined trait IntFunction

scala> def sum[T](as: Traversable[T])(f: IntFunction[T]) = { var sum = 0; as foreach (a => sum += f(a)); sum }
sum: [T](as: Traversable[T])(f: IntFunction[T])Int

scala> sum(List("a", "bc"))(_.length)
res2: Int = 3

No boxing is needed here.

@retronym Issue was closed in 2014, but now that we have Java 8 java.util.function package with all predefined SAM interfaces, can we look into the possibility of translating "partially specialized" FunctionXs into the SAM type objects? E.g.

case class Foo(i: Int)
def getFooField(foo: Foo, f: Foo=>Int): Int = f(foo)

Instead of compiling into

getFooField:(LFoo;Lscala/Function1;)Ljava.lang.Integer    //Int is boxed when invokevirtual

can the compiler compile it into

getFooField:(LFoo;Ljava.util.function.ToIntFunction):I    //No boxing for returned Int

We could use self-defined SAM, or even Java SAM types, but Scala should have its own set, or being able to translate it under the hood.

@texasbruce The compiler logic that would decide to use such an interface is the buggy part of Scala's specialization transform. We don't see a path forward to getting it working as its one of the trickiest areas of the compiler even before dealing with partial specialization.