[base] Add iterator_range helper class.

src/base/iterator.h

+// Copyright 2014 the V8 project authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+#ifndef V8_BASE_ITERATOR_H_
+#define V8_BASE_ITERATOR_H_
+
+#include <iterator>
+
+#include "src/base/macros.h"
+
+namespace v8 {
+namespace base {
+
+// The intention of the base::iterator_range class is to encapsulate two
+// iterators so that the range defined by the iterators can be used like
+// a regular STL container (actually only a subset of the full container
+// functionality is available usually).
+template <typename ForwardIterator>
+class iterator_range {
+ public:
+  typedef ForwardIterator iterator;
+  typedef ForwardIterator const_iterator;
+  typedef typename std::iterator_traits<iterator>::pointer pointer;
+  typedef typename std::iterator_traits<iterator>::reference reference;
+  typedef typename std::iterator_traits<iterator>::value_type value_type;
+  typedef
+      typename std::iterator_traits<iterator>::difference_type difference_type;
+
+  iterator_range() : begin_(), end_() {}
+  template <typename ForwardIterator2>
+  iterator_range(ForwardIterator2 const& begin, ForwardIterator2 const& end)
+      : begin_(begin), end_(end) {}
+
+  iterator begin() { return begin_; }
+  iterator end() { return end_; }
+  const_iterator begin() const { return begin_; }
+  const_iterator end() const { return end_; }
+  const_iterator cbegin() const { return begin_; }
+  const_iterator cend() const { return end_; }
+
+  bool empty() const { return cbegin() == cend(); }
+
+  // Random Access iterators only.
+  reference operator[](difference_type n) { return begin()[n]; }
+  difference_type size() const { return cend() - cbegin(); }
+
+ private:
+  const_iterator const begin_;
+  const_iterator const end_;
+};
+
+}  // namespace base
+}  // namespace v8
+
+#endif  // V8_BASE_ITERATOR_H_