Implement FixedSizeArray for all fixed size arrays

Do so by using the fact that fixed size arrays (like `[u8; 8]` can be coerced
to slices `&[u8]`, this is expressed through the trait `Unsize<[T]>` that all
fixed size arrays implement.

src/libcore/array.rs

@@ -26,7 +26,7 @@ use default::Default;
 use fmt;
 use hash::{Hash, self};
 use iter::IntoIterator;
-use marker::{Copy, Sized};
+use marker::{Copy, Sized, Unsize};
 use option::Option;
 use slice::{Iter, IterMut, SliceExt};
 
@@ -41,21 +41,21 @@ pub trait FixedSizeArray<T> {
     fn as_mut_slice(&mut self) -> &mut [T];
 }
 
+impl<T, A: Unsize<[T]>> FixedSizeArray<T> for A {
+    #[inline]
+    fn as_slice(&self) -> &[T] {
+        self
+    }
+    #[inline]
+    fn as_mut_slice(&mut self) -> &mut [T] {
+        self
+    }
+}
+
 // macro for implementing n-ary tuple functions and operations
 macro_rules! array_impls {
     ($($N:expr)+) => {
         $(
-            impl<T> FixedSizeArray<T> for [T; $N] {
-                #[inline]
-                fn as_slice(&self) -> &[T] {
-                    &self[..]
-                }
-                #[inline]
-                fn as_mut_slice(&mut self) -> &mut [T] {
-                    &mut self[..]
-                }
-            }
-
             impl<T> AsRef<[T]> for [T; $N] {
                 #[inline]
                 fn as_ref(&self) -> &[T] {

src/libcoretest/array.rs

@@ -0,0 +1,28 @@
+// Copyright 2014 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.
+use core::array::FixedSizeArray;
+
+#[test]
+fn fixed_size_array() {
+    let mut array = [0; 64];
+    let mut zero_sized = [(); 64];
+    let mut empty_array = [0; 0];
+    let mut empty_zero_sized = [(); 0];
+
+    assert_eq!(FixedSizeArray::as_slice(&array).len(), 64);
+    assert_eq!(FixedSizeArray::as_slice(&zero_sized).len(), 64);
+    assert_eq!(FixedSizeArray::as_slice(&empty_array).len(), 0);
+    assert_eq!(FixedSizeArray::as_slice(&empty_zero_sized).len(), 0);
+
+    assert_eq!(FixedSizeArray::as_mut_slice(&mut array).len(), 64);
+    assert_eq!(FixedSizeArray::as_mut_slice(&mut zero_sized).len(), 64);
+    assert_eq!(FixedSizeArray::as_mut_slice(&mut empty_array).len(), 0);
+    assert_eq!(FixedSizeArray::as_mut_slice(&mut empty_zero_sized).len(), 0);
+}

src/libcoretest/lib.rs

@@ -15,11 +15,12 @@
 #![feature(const_fn)]
 #![feature(core)]
 #![feature(core_float)]
+#![feature(dec2flt)]
+#![feature(decode_utf16)]
+#![feature(fixed_size_array)]
 #![feature(float_extras)]
 #![feature(float_from_str_radix)]
 #![feature(flt2dec)]
-#![feature(dec2flt)]
-#![feature(decode_utf16)]
 #![feature(fmt_radix)]
 #![feature(iter_arith)]
 #![feature(iter_arith)]
@@ -48,6 +49,7 @@ extern crate rustc_unicode;
 extern crate rand;
 
 mod any;
+mod array;
 mod atomic;
 mod cell;
 mod char;