Add list.removeAt method.

lib/core/list.dart

 // Copyright (c) 2011, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
 /**
  * A [List] is an indexable collection with a length. It can be of
  * fixed size or extendable.
  */
 interface List<E> extends Collection<E> default ListImplementation<E> {
 
@@ skipping 77 matching lines @@
    */
   int lastIndexOf(E element, [int start]);
 
   /**
    * Removes all elements in the list. The length of the list
    * becomes zero. Throws an [UnsupportedOperationException] if
    * the list is not extendable.
    */
   void clear();
 
+  /**  
+   * Removes the element at position[index] from the list.

[ngeoffray, 2012/09/20 09:16:24]

FYI: we did not have removeAt initially because it makes it too simple to use,
without showing that this is an expensive operation. So we have removeRange
already that does removeAt, but with the 'Range' in the name, it *feels*
expensive.

[Lasse Reichstein Nielsen, 2012/09/20 10:50:29]

Performance through inconvenience :)
I don't think it's going to work in the long run. I'd rather provide the methods
that people want to call than make it hard to get the job done (even if it's
done slowly).

+   *
+   * This reduces the length of the list by one and moves
+   * all later elements down by one position.
+   * Returns the removed element.
+   * Throws a [UnsupportedOperationException] if the list, or the 
+   * length of the list, cannot be changed.
+   */
+  E removeAt(int index);
+
   /**
    * Pops and returns the last element of the list.
    * Throws a [UnsupportedOperationException] if the length of the
    * list cannot be changed.
+   * 
    */
   E removeLast();
 
   /**
    * Returns the last element of the list, or throws an out of bounds
    * exception if the list is empty.
    */
   E last();
 
   /**
@@ skipping 35 matching lines @@
    * not extendable.
    * If [length] is 0, this method does not do anything.
    * If [start] is the length of the list, this method inserts the
    * range at the end of the list.
    * Throws an [IllegalArgumentException] if [length] is negative.
    * Throws an [IndexOutOfRangeException] if [start] is negative or if
    * [start] is greater than the length of the list.
    */
   void insertRange(int start, int length, [E initialValue]);
 }