Implement defaults for associated types

src/test/run-pass/default-associated-types.rs

@@ -0,0 +1,30 @@
+// Copyright 2015 The Rust Project Developers. See the COPYRIGHT
+// file at the top-level directory of this distribution and at
+// http://rust-lang.org/COPYRIGHT.
+//
+// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
+// http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
+// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
+// option. This file may not be copied, modified, or distributed
+// except according to those terms.
+
+trait Foo<T> {
+    type Out = T;
+    fn foo(&self) -> Self::Out;
+}
+
+impl Foo<u32> for () {
+    fn foo(&self) -> u32 {
+        4u32
+    }
+}
+
+impl Foo<u64> for bool {
+    type Out = ();
+    fn foo(&self) {}
+}
+
+fn main() {
+    assert_eq!(<() as Foo<u32>>::foo(&()), 4u32);
+    assert_eq!(<bool as Foo<u64>>::foo(&true), ());
+}