core: Remove Self: Sized from Iterator::nth

It is an unnecessary restriction; nth neither needs self to be sized
nor needs to be exempted from the trait object.

It increases the utility of the nth method, because type specific
implementations are available through `&mut I` or through an iterator
trait object.

It is a backwards compatible change due to the special cases of the
`where Self: Sized` bound; it was already optional to include this bound
in `Iterator` implementations.

1 files changed, 3 insertions, 0 deletions

diff --git a/src/liballoc/boxed.rs b/src/liballoc/boxed.rs
index 28f4dda1408..d10d7a5e58d 100644
--- a/src/liballoc/boxed.rs
+++ b/src/liballoc/boxed.rs
@@ -524,6 +524,9 @@ impl<I: Iterator + ?Sized> Iterator for Box<I> {
     fn size_hint(&self) -> (usize, Option<usize>) {
         (**self).size_hint()
     }
+    fn nth(&mut self, n: usize) -> Option<I::Item> {
+        (**self).nth(n)
+    }
 }
 #[stable(feature = "rust1", since = "1.0.0")]
 impl<I: DoubleEndedIterator + ?Sized> DoubleEndedIterator for Box<I> {