Write option::chain and result::chain with match move

Closes #3590

Author: catamorphism

src/libcore/option.rs

@@ -119,11 +119,9 @@ pub pure fn chain<T, U>(opt: Option<T>,
      * function that returns an option.
      */
 
-    // XXX write with move match
-    if opt.is_some() {
-        f(unwrap(opt))
-    } else {
-        None
+    match move opt {
+        Some(move t) => f(t),
+        None => None
     }
 }
 

src/libcore/result.rs

@@ -105,11 +105,9 @@ pub pure fn to_either<T: Copy, U: Copy>(res: &Result<U, T>)
  */
 pub fn chain<T, U: Copy, V: Copy>(res: Result<T, V>, op: fn(t: T)
     -> Result<U, V>) -> Result<U, V> {
-    // XXX: Should be writable with move + match
-    if res.is_ok() {
-        op(unwrap(res))
-    } else {
-        Err(unwrap_err(res))
+    match move res {
+        Ok(move t) => op(t),
+        Err(move e) => Err(e)
     }
 }