Make vec::pop efficient

Author: marijnh

src/libcore/vec.rs

@@ -294,27 +294,18 @@ fn shift<T: copy>(&v: [const T]) -> T {
     ret e;
 }
 
-// TODO: Write this, unsafely, in a way that's not O(n).
 /*
 Function: pop
 
 Remove the last element from a vector and return it
 */
-fn pop<T: copy>(&v: [const T]) -> T {
+fn pop<T>(&v: [const T]) -> T unsafe {
     let ln = len(v);
-    assert (ln > 0u);
-    ln -= 1u;
-    let e = v[ln];
-    v = slice(v, 0u, ln);
-    ret e;
-// FIXME use this implementation after the next snapshot (27.01.2012)
-/*  let new_ln = len(v) - 1u;
-    assert (new_ln > 0u);
-    let valptr = ptr::mut_addr_of(v[new_ln]);
+    assert ln > 0u;
+    let valptr = ptr::mut_addr_of(v[ln - 1u]);
     let val <- *valptr;
-    unsafe::set_len(v, new_ln);
+    unsafe::set_len(v, ln - 1u);
     val
-*/
 }
 
 /*