Add Default trait for AtomicBool, AtomicIsize and AtomicUsize

src/libcore/atomic.rs

@@ -78,12 +78,20 @@ use intrinsics;
 use cell::UnsafeCell;
 use marker::PhantomData;
 
+use default::Default;
+
 /// A boolean type which can be safely shared between threads.
 #[stable(feature = "rust1", since = "1.0.0")]
 pub struct AtomicBool {
     v: UnsafeCell<usize>,
 }
 
+impl Default for AtomicBool {
+    fn default() -> AtomicBool {
+        ATOMIC_BOOL_INIT
+    }
+}
+
 unsafe impl Sync for AtomicBool {}
 
 /// A signed integer type which can be safely shared between threads.
@@ -92,6 +100,12 @@ pub struct AtomicIsize {
     v: UnsafeCell<isize>,
 }
 
+impl Default for AtomicIsize {
+    fn default() -> AtomicIsize {
+        ATOMIC_ISIZE_INIT
+    }
+}
+
 unsafe impl Sync for AtomicIsize {}
 
 /// An unsigned integer type which can be safely shared between threads.
@@ -100,6 +114,12 @@ pub struct AtomicUsize {
     v: UnsafeCell<usize>,
 }
 
+impl Default for AtomicUsize {
+    fn default() -> AtomicUsize {
+        ATOMIC_USIZE_INIT
+    }
+}
+
 unsafe impl Sync for AtomicUsize {}
 
 /// A raw pointer type which can be safely shared between threads.