Extend base::Reversed to support iterating arrays

C++11's range-based for syntax supports iterating arrays,
so it makes sense to support arrays in base::Reversed too.

Review URL: https://codereview.chromium.org/1360423002

Cr-Commit-Position: refs/heads/master@{#354181}

base/containers/adapters.h

@@ -5,6 +5,10 @@
 #ifndef BASE_CONTAINERS_ADAPTERS_H_
 #define BASE_CONTAINERS_ADAPTERS_H_
 
+#include <stddef.h>
+
+#include <iterator>
+
 #include "base/macros.h"
 
 namespace base {
@@ -15,11 +19,13 @@ namespace internal {
 template <typename T>
 class ReversedAdapter {
  public:
-  typedef decltype(static_cast<T*>(nullptr)->rbegin()) Iterator;
+  using Iterator = decltype(static_cast<T*>(nullptr)->rbegin());
 
   explicit ReversedAdapter(T& t) : t_(t) {}
   ReversedAdapter(const ReversedAdapter& ra) : t_(ra.t_) {}
 
+  // TODO(mdempsky): Once we can use C++14 library features, use std::rbegin
+  // and std::rend instead, so we can remove the specialization below.
   Iterator begin() const { return t_.rbegin(); }
   Iterator end() const { return t_.rend(); }
 
@@ -29,6 +35,23 @@ class ReversedAdapter {
   DISALLOW_ASSIGN(ReversedAdapter);
 };
 
+template <typename T, size_t N>
+class ReversedAdapter<T[N]> {
+ public:
+  using Iterator = std::reverse_iterator<T*>;
+
+  explicit ReversedAdapter(T (&t)[N]) : t_(t) {}
+  ReversedAdapter(const ReversedAdapter& ra) : t_(ra.t_) {}
+
+  Iterator begin() const { return Iterator(&t_[N]); }
+  Iterator end() const { return Iterator(&t_[0]); }
+
+ private:
+  T (&t_)[N];
+
+  DISALLOW_ASSIGN(ReversedAdapter);
+};
+
 }  // namespace internal
 
 // Reversed returns a container adapter usable in a range-based "for" statement

base/containers/adapters_unittest.cc

@@ -25,7 +25,19 @@ TEST(AdaptersTest, Reversed) {
   EXPECT_EQ(101, v[2]);
 }
 
-TEST(AdaptersTest, ConstReversed) {
+TEST(AdaptersTest, ReversedArray) {
+  int v[3] = {3, 2, 1};
+  int j = 0;
+  for (int& i : base::Reversed(v)) {
+    EXPECT_EQ(++j, i);
+    i += 100;
+  }
+  EXPECT_EQ(103, v[0]);
+  EXPECT_EQ(102, v[1]);
+  EXPECT_EQ(101, v[2]);
+}
+
+TEST(AdaptersTest, ReversedConst) {
   std::vector<int> v;
   v.push_back(3);
   v.push_back(2);