auto merge of #13963 : kballard/rust/remove_owned_vec_from_iterator, r=pcwalton

With `~[T]` no longer growable, the `FromIterator` impl for `~[T]` doesn't make
much sense. Not only that, but nearly everywhere it is used is to convert from
a `Vec<T>` into a `~[T]`, for the sake of maintaining existing APIs. This turns
out to be a performance loss, as it means every API that returns `~[T]`, even a
supposedly non-copying one, is in fact doing extra allocations and memcpy's.
Even `&[T].to_owned()` is going through `Vec<T>` first.

Remove the `FromIterator` impl for `~[T]`, and adjust all the APIs that relied
on it to start using `Vec<T>` instead. This includes rewriting
`&[T].to_owned()` to be more efficient, among other performance wins.

Also add a new mechanism to go from `Vec<T>` -> `~[T]`, just in case anyone
truly needs that, using the new trait `FromVec`.

[breaking-change]

2 files changed, 5 insertions, 5 deletions

diff --git a/src/libstd/sync/arc.rs b/src/libstd/sync/arc.rs
index d277c514e44..676c836c459 100644
--- a/src/libstd/sync/arc.rs
+++ b/src/libstd/sync/arc.rs
@@ -69,14 +69,14 @@ impl<T: Send> UnsafeArc<T> {
 
     /// As new(), but returns a vector of as many pre-cloned handles as
     /// requested.
-    pub fn newN(data: T, num_handles: uint) -> ~[UnsafeArc<T>] {
+    pub fn newN(data: T, num_handles: uint) -> Vec<UnsafeArc<T>> {
         unsafe {
             if num_handles == 0 {
-                box [] // need to free data here
+                vec![] // need to free data here
             } else {
                 let ptr = new_inner(data, num_handles);
                 let v = Vec::from_fn(num_handles, |_| UnsafeArc { data: ptr });
-                v.move_iter().collect()
+                v
             }
         }
     }
diff --git a/src/libstd/sync/deque.rs b/src/libstd/sync/deque.rs
index d06062f02ac..8dfd691e6ff 100644
--- a/src/libstd/sync/deque.rs
+++ b/src/libstd/sync/deque.rs
@@ -407,7 +407,7 @@ mod tests {
     use rand::Rng;
     use sync::atomics::{AtomicBool, INIT_ATOMIC_BOOL, SeqCst,
                         AtomicUint, INIT_ATOMIC_UINT};
-    use slice;
+    use vec;
 
     #[test]
     fn smoke() {
@@ -603,7 +603,7 @@ mod tests {
         let mut pool = BufferPool::<(int, uint)>::new();
         let (mut w, s) = pool.deque();
 
-        let (threads, hits) = slice::unzip(range(0, NTHREADS).map(|_| {
+        let (threads, hits) = vec::unzip(range(0, NTHREADS).map(|_| {
             let s = s.clone();
             let unique_box = box AtomicUint::new(0);
             let thread_box = unsafe {