Add base::get to support rvalue-reference tuple

base/tuple.h

 // Copyright (c) 2011 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 // Use std::tuple as tuple type. This file contains helper functions for
 // working with std::tuples.
 // The functions DispatchToMethod and DispatchToFunction take a function pointer
 // or instance and method pointer, and unpack a tuple into arguments to the
 // call.
 //
@@ skipping 86 matching lines @@
 struct MakeIndexSequenceImpl<0, Ns...> {
   using Type = IndexSequence<Ns...>;
 };
 
 template <size_t N, size_t... Ns>
 struct MakeIndexSequenceImpl<N, Ns...>
     : MakeIndexSequenceImpl<N - 1, N - 1, Ns...> {};
 
 #endif  // defined(OS_WIN) && defined(_PREFAST_)
 
+// std::get() in <=libstdc++-4.6 returns an lvalue-reference for
+// rvalue-reference of a tuple, where an rvalue-reference is expected.
+template <size_t I, typename... Ts>
+typename std::tuple_element<I, std::tuple<Ts...>>::type&& get(
+    std::tuple<Ts...>&& t) {
+  using ElemType = typename std::tuple_element<I, std::tuple<Ts...>>::type;
+  return std::forward<ElemType>(std::get<I>(t));
+}
+
+template <size_t I, typename T>
+auto get(T& t) -> decltype(std::get<I>(t)) {
+  return std::get<I>(t);
+}
+
 template <size_t N>
 using MakeIndexSequence = typename MakeIndexSequenceImpl<N>::Type;
 
 // Dispatchers ----------------------------------------------------------------
 //
 // Helper functions that call the given method on an object, with the unpacked
 // tuple arguments.  Notice that they all have the same number of arguments,
 // so you need only write:
 //   DispatchToMethod(object, &Object::method, args);
 // This is very useful for templated dispatchers, since they don't need to know
@@ skipping 55 matching lines @@
                              const std::tuple<InTs...>& in,
                              std::tuple<OutTs...>* out) {
   DispatchToMethodImpl(obj, method, in, out,
                        MakeIndexSequence<sizeof...(InTs)>(),
                        MakeIndexSequence<sizeof...(OutTs)>());
 }
 
 }  // namespace base
 
 #endif  // BASE_TUPLE_H_