Restore Decodable impl for ~[T]

Bring back the Decodable impl for ~[T], this time using FromVec. It's
still not recommended that anyone use this, but at least it's available
if necessary.

Author: lilyball

src/libserialize/serialize.rs

@@ -451,6 +451,21 @@ impl<E, S:Encoder<E>,T:Encodable<S, E>> Encodable<S, E> for ~[T] {
     }
 }
 
+impl<E, D:Decoder<E>,T:Decodable<D, E>> Decodable<D, E> for ~[T] {
+    fn decode(d: &mut D) -> Result<~[T], E> {
+        use std::vec::FromVec;
+
+        d.read_seq(|d, len| {
+            let mut v: Vec<T> = Vec::with_capacity(len);
+            for i in range(0, len) {
+                v.push(try!(d.read_seq_elt(i, |d| Decodable::decode(d))));
+            }
+            let k: ~[T] = FromVec::from_vec(v);
+            Ok(k)
+        })
+    }
+}
+
 impl<E, S:Encoder<E>,T:Encodable<S, E>> Encodable<S, E> for Vec<T> {
     fn encode(&self, s: &mut S) -> Result<(), E> {
         s.emit_seq(self.len(), |s| {