Create generic check methods for RangeError causing checks.

sdk/lib/collection/iterable.dart

 // Copyright (c) 2012, 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.
 
 part of dart.collection;
 
 /**
  * This [Iterable] mixin implements all [Iterable] members except `iterator`.
  *
  * All other methods are implemented in terms of `iterator`.
@@ skipping 168 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);
   }
 
+
   String toString() => IterableBase.iterableToShortString(this, '(', ')');
 }
 
 /**
  * Base class for implementing [Iterable].
  *
  * This class implements all methods of [Iterable] except [Iterable.iterator]
  * in terms of `iterator`.
  */
 abstract class IterableBase<E> implements Iterable<E> {
@@ skipping 165 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);
   }
 
   /**
    * Returns a string representation of (some of) the elements of `this`.
    *
    * Elements are represented by their own `toString` results.
    *
    * The representation always contains the first three elements.
    * If there are less than a hundred elements in the iterable, it also
    * contains the last two elements.
@@ skipping 188 matching lines @@
         length += ELLIPSIS_SIZE + OVERHEAD;
       }
     }
     if (elision != null) {
       parts.add(elision);
     }
     parts.add(penultimateString);
     parts.add(ultimateString);
   }
 }