Create generic check methods for RangeError causing checks.

sdk/lib/collection/set.dart

 // Copyright (c) 2014, 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.
 
 /**
  * Base implementations of [Set].
  */
 part of dart.collection;
 
 /**
@@ skipping 253 matching lines @@
         }
         result = element;
         foundMatching = true;
       }
     }
     if (foundMatching) return result;
     throw IterableElementError.noElement();
   }
 
   E elementAt(int index) {
-    if (index is! int || index < 0) throw new RangeError.value(index);
-    int remaining = index;
+    if (index is! int) throw new ArgumentError.notNull("index");
+    RangeError.checkNotNegative(index, "index");
+    int elementIndex = 0;
     for (E element in this) {
-      if (remaining == 0) return element;
-      remaining--;
+      if (index == elementIndex) return element;
+      elementIndex++;
     }
-    throw new RangeError.value(index);
+    throw new RangeError.index(index, this, "index", null, elementIndex);
   }
 }
 
 /**
  * Base implementation of [Set].
  *
  * This class provides a base implementation of a `Set` that depends only
  * on the abstract members: [add], [contains], [lookup], [remove],
  * [iterator], [length] and [toSet].
  *
@@ skipping 10 matching lines @@
 abstract class SetBase<E> extends SetMixin<E> {
   /**
    * Convert a `Set` to a string as `{each, element, as, string}`.
    *
    * Handles circular references where converting one of the elements
    * to a string ends up converting [set] to a string again.
    */
   static String setToString(Set set) =>
       IterableBase.iterableToFullString(set, '{', '}');
 }