Bug 1127044 part 1 - Add IteratorTraits facility. r=waldo

mfbt/IteratorTraits.h

@@ -0,0 +1,39 @@
+/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* vim: set ts=8 sts=2 et sw=2 tw=80: */
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+/* Iterator traits to expose a value type and a difference type */
+
+#ifndef mozilla_IteratorTraits_h
+#define mozilla_IteratorTraits_h
+
+#include <stddef.h>
+
+namespace mozilla {
+
+template<typename Iterator>
+struct IteratorTraits
+{
+  typedef typename Iterator::ValueType ValueType;
+  typedef typename Iterator::DifferenceType DifferenceType;
+};
+
+template<typename T>
+struct IteratorTraits<T*>
+{
+  typedef T ValueType;
+  typedef ptrdiff_t DifferenceType;
+};
+
+template<typename T>
+struct IteratorTraits<const T*>
+{
+  typedef const T ValueType;
+  typedef ptrdiff_t DifferenceType;
+};
+
+} // namespace mozilla
+
+#endif // mozilla_IteratorTraits_h

mfbt/moz.build

@@ -38,6 +38,7 @@ EXPORTS.mozilla = [
     'HashFunctions.h',
     'IntegerPrintfMacros.h',
     'IntegerTypeTraits.h',
+    'IteratorTraits.h',
     'JSONWriter.h',
     'Likely.h',
     'LinkedList.h',