[base] Add iterator_range helper class.

TEST=unittests
R=titzer@chromium.org

Review URL: https://codereview.chromium.org/810683003

Cr-Commit-Position: refs/heads/master@{#25834}

BUILD.gn

@@ -1262,6 +1262,7 @@ source_set("v8_libbase") {
     "src/base/flags.h",
     "src/base/functional.cc",
     "src/base/functional.h",
+    "src/base/iterator.h",
     "src/base/lazy-instance.h",
     "src/base/logging.cc",
     "src/base/logging.h",

src/base/iterator.h

@@ -0,0 +1,56 @@
+// 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_

test/unittests/base/iterator-unittest.cc

@@ -0,0 +1,61 @@
+// 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.
+
+#include "src/base/iterator.h"
+
+#include <deque>
+
+#include "test/unittests/test-utils.h"
+
+namespace v8 {
+namespace base {
+
+TEST(IteratorTest, IteratorRangeEmpty) {
+  base::iterator_range<char*> r;
+  EXPECT_EQ(r.begin(), r.end());
+  EXPECT_EQ(r.end(), r.cend());
+  EXPECT_EQ(r.begin(), r.cbegin());
+  EXPECT_TRUE(r.empty());
+  EXPECT_EQ(0, r.size());
+}
+
+
+TEST(IteratorTest, IteratorRangeArray) {
+  int array[10] = {0, 1, 2, 3, 4, 5, 6, 7, 8, 9};
+  base::iterator_range<int*> r1(&array[0], &array[10]);
+  for (auto i : r1) {
+    EXPECT_EQ(array[i], i);
+  }
+  EXPECT_EQ(10, r1.size());
+  EXPECT_FALSE(r1.empty());
+  for (size_t i = 0; i < arraysize(array); ++i) {
+    EXPECT_EQ(r1[i], array[i]);
+  }
+  base::iterator_range<int*> r2(&array[0], &array[0]);
+  EXPECT_EQ(0, r2.size());
+  EXPECT_TRUE(r2.empty());
+  for (auto i : array) {
+    EXPECT_EQ(r2.end(), std::find(r2.begin(), r2.end(), i));
+  }
+}
+
+
+TEST(IteratorTest, IteratorRangeDeque) {
+  typedef std::deque<unsigned> C;
+  C c;
+  c.push_back(1);
+  c.push_back(2);
+  c.push_back(2);
+  base::iterator_range<typename C::iterator> r(c.begin(), c.end());
+  EXPECT_EQ(3, r.size());
+  EXPECT_FALSE(r.empty());
+  EXPECT_TRUE(c.begin() == r.begin());
+  EXPECT_TRUE(c.end() == r.end());
+  EXPECT_EQ(0, std::count(r.begin(), r.end(), 0));
+  EXPECT_EQ(1, std::count(r.begin(), r.end(), 1));
+  EXPECT_EQ(2, std::count(r.begin(), r.end(), 2));
+}
+
+}  // namespace base
+}  // namespace v8

test/unittests/unittests.gyp

@@ -28,6 +28,7 @@
         'base/division-by-constant-unittest.cc',
         'base/flags-unittest.cc',
         'base/functional-unittest.cc',
+        'base/iterator-unittest.cc',
         'base/platform/condition-variable-unittest.cc',
         'base/platform/mutex-unittest.cc',
         'base/platform/platform-unittest.cc',

tools/gyp/v8.gyp

@@ -1263,6 +1263,7 @@
         '../../src/base/flags.h',
         '../../src/base/functional.cc',
         '../../src/base/functional.h',
+        '../../src/base/iterator.h',
         '../../src/base/lazy-instance.h',
         '../../src/base/logging.cc',
         '../../src/base/logging.h',