collections: Add missing Default impls

Add Default impls for TreeMap, TreeSet, SmallIntMap, BitvSet, DList,
PriorityQueue, RingBuf, TrieMap, and TrieSet.

src/libcollections/bitv.rs

@@ -13,6 +13,7 @@
 use core::prelude::*;
 
 use core::cmp;
+use core::default::Default;
 use core::fmt;
 use core::iter::{Enumerate, Repeat, Map, Zip};
 use core::ops;
@@ -698,6 +699,11 @@ pub struct BitvSet {
     bitv: BigBitv
 }
 
+impl Default for BitvSet {
+    #[inline]
+    fn default() -> BitvSet { BitvSet::new() }
+}
+
 impl BitvSet {
     /// Creates a new bit vector set with initially no contents
     pub fn new() -> BitvSet {

src/libcollections/dlist.rs

@@ -24,6 +24,7 @@
 use core::prelude::*;
 
 use alloc::owned::Box;
+use core::default::Default;
 use core::fmt;
 use core::iter;
 use core::mem;
@@ -262,6 +263,11 @@ fn pop_back(&mut self) -> Option<T> {
     }
 }
 
+impl<T> Default for DList<T> {
+    #[inline]
+    fn default() -> DList<T> { DList::new() }
+}
+
 impl<T> DList<T> {
     /// Create an empty DList
     #[inline]

src/libcollections/priority_queue.rs

@@ -14,6 +14,7 @@
 
 use core::prelude::*;
 
+use core::default::Default;
 use core::mem::{zeroed, replace, swap};
 use core::ptr;
 
@@ -37,6 +38,11 @@ impl<T: Ord> Mutable for PriorityQueue<T> {
     fn clear(&mut self) { self.data.truncate(0) }
 }
 
+impl<T: Ord> Default for PriorityQueue<T> {
+    #[inline]
+    fn default() -> PriorityQueue<T> { PriorityQueue::new() }
+}
+
 impl<T: Ord> PriorityQueue<T> {
     /// An iterator visiting all values in underlying vector, in
     /// arbitrary order.

src/libcollections/ringbuf.rs

@@ -16,6 +16,7 @@
 use core::prelude::*;
 
 use core::cmp;
+use core::default::Default;
 use core::fmt;
 use core::iter::RandomAccessIterator;
 
@@ -112,6 +113,11 @@ fn push_back(&mut self, t: T) {
     }
 }
 
+impl<T> Default for RingBuf<T> {
+    #[inline]
+    fn default() -> RingBuf<T> { RingBuf::new() }
+}
+
 impl<T> RingBuf<T> {
     /// Create an empty RingBuf
     pub fn new() -> RingBuf<T> {

src/libcollections/smallintmap.rs

@@ -17,6 +17,7 @@
 
 use core::prelude::*;
 
+use core::default::Default;
 use core::fmt;
 use core::iter::{Enumerate, FilterMap};
 use core::mem::replace;
@@ -114,6 +115,11 @@ fn pop(&mut self, key: &uint) -> Option<V> {
     }
 }
 
+impl<V> Default for SmallIntMap<V> {
+    #[inline]
+    fn default() -> SmallIntMap<V> { SmallIntMap::new() }
+}
+
 impl<V> SmallIntMap<V> {
     /// Create an empty SmallIntMap
     pub fn new() -> SmallIntMap<V> { SmallIntMap{v: vec!()} }

src/libcollections/treemap.rs

@@ -15,6 +15,7 @@
 use core::prelude::*;
 
 use alloc::owned::Box;
+use core::default::Default;
 use core::fmt;
 use core::fmt::Show;
 use core::iter::Peekable;
@@ -135,6 +136,11 @@ fn pop(&mut self, key: &K) -> Option<V> {
     }
 }
 
+impl<K: Ord, V> Default for TreeMap<K,V> {
+    #[inline]
+    fn default() -> TreeMap<K, V> { TreeMap::new() }
+}
+
 impl<K: Ord, V> TreeMap<K, V> {
     /// Create an empty TreeMap
     pub fn new() -> TreeMap<K, V> { TreeMap{root: None, length: 0} }
@@ -633,6 +639,11 @@ fn insert(&mut self, value: T) -> bool { self.map.insert(value, ()) }
     fn remove(&mut self, value: &T) -> bool { self.map.remove(value) }
 }
 
+impl<T: Ord> Default for TreeSet<T> {
+    #[inline]
+    fn default() -> TreeSet<T> { TreeSet::new() }
+}
+
 impl<T: Ord> TreeSet<T> {
     /// Create an empty TreeSet
     #[inline]

src/libcollections/trie.rs

@@ -13,6 +13,7 @@
 use core::prelude::*;
 
 use alloc::owned::Box;
+use core::default::Default;
 use core::mem::zeroed;
 use core::mem;
 use core::uint;
@@ -105,6 +106,11 @@ fn pop(&mut self, key: &uint) -> Option<T> {
     }
 }
 
+impl<T> Default for TrieMap<T> {
+    #[inline]
+    fn default() -> TrieMap<T> { TrieMap::new() }
+}
+
 impl<T> TrieMap<T> {
     /// Create an empty TrieMap
     #[inline]
@@ -332,6 +338,11 @@ fn remove(&mut self, value: &uint) -> bool {
     }
 }
 
+impl Default for TrieSet {
+    #[inline]
+    fn default() -> TrieSet { TrieSet::new() }
+}
+
 impl TrieSet {
     /// Create an empty TrieSet
     #[inline]