Extend base::Reversed to support iterating arrays

base/containers/adapters.h

Index: base/containers/adapters.h
diff --git a/base/containers/adapters.h b/base/containers/adapters.h
index cc151fc2468bfd630f80e959437fe95fb2d3724b..c0594cd38532077480818169241258f44e2082e2 100644
--- a/base/containers/adapters.h
+++ b/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 +35,29 @@ class ReversedAdapter {
   DISALLOW_ASSIGN(ReversedAdapter);
 };
 
+template <typename T, size_t N>
+class ReversedAdapter<T[N]> {
+ public:
+  using Iterator = std::reverse_iterator<T*>;
+
+  // TODO(mdempsky): clang-format rewrites this as "T(&t)[N]" (b/24351059).

[danakj, 2015/10/14 23:21:05]

Thanks for filing. Has the fix rolled to chrome yet?

[mdempsky, 2015/10/14 23:39:11]

Not yet, as far as I can tell.  Still, I removed the clang-format directives
optimistically hoping that it will be rolled before the next time someone has to
work in this file.

+  // clang-format off
+  explicit ReversedAdapter(T (&t)[N]) : t_(t) {}
+  // clang-format on
+  ReversedAdapter(const ReversedAdapter& ra) : t_(ra.t_) {}
+
+  Iterator begin() const { return Iterator(&t_[N]); }
+  Iterator end() const { return Iterator(&t_[0]); }
+
+ private:
+  // See above.
+  // clang-format off
+  T (&t_)[N];
+  // clang-format on
+
+  DISALLOW_ASSIGN(ReversedAdapter);
+};
+
 }  // namespace internal
 
 // Reversed returns a container adapter usable in a range-based "for" statement