WIP: base::Bind for rvalue references.

base/callback_internal.h

 // Copyright (c) 2012 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.
 
 // This file contains utility functions and classes that help the
 // implementation, and management of the Callback objects.
 
 #ifndef BASE_CALLBACK_INTERNAL_H_
 #define BASE_CALLBACK_INTERNAL_H_
 
@@ skipping 109 matching lines @@
 // extract a suitable type for storing and forwarding arguments.
 //
 // In particular, it strips off references, and converts arrays to
 // pointers for storage; and it avoids accidentally trying to create a
 // "reference of a reference" if the argument is a reference type.
 //
 // This array type becomes an issue for storage because we are passing bound
 // parameters by const reference. In this case, we end up passing an actual
 // array type in the initializer list which C++ does not allow.  This will
 // break passing of C-string literals.
-template <typename T>
+template <typename T, typename = void>
 struct CallbackParamTraits
-    : std::conditional<IsMoveOnlyType<T>::value,
-         CallbackParamTraitsForMoveOnlyType<T>,
-         CallbackParamTraitsForNonMoveOnlyType<T>>::type {
+    : std::conditional<is_move_only<typename std::decay<T>::type>::value,
+                       CallbackParamTraitsForMoveOnlyType<T>,
+                       CallbackParamTraitsForNonMoveOnlyType<T>>::type {
 };
 
 template <typename T>
+struct CallbackParamTraits<
+    T,
+    typename std::conditional<false,
+                              typename std::decay<T>::type::value_type,
+                              void>::type>
+    : public std::conditional<
+          base::is_move_only<typename std::decay<T>::type>::value ||
+              base::is_move_only<
+                  typename std::decay<T>::type::value_type>::value,
+          CallbackParamTraitsForMoveOnlyType<T>,
+          CallbackParamTraitsForNonMoveOnlyType<T>>::type {
+};
+
+template <typename T>
 struct CallbackParamTraitsForNonMoveOnlyType {
   typedef const T& ForwardType;
   typedef T StorageType;
 };
 
 // The Storage should almost be impossible to trigger unless someone manually
 // specifies type of the bind parameters.  However, in case they do,
 // this will guard against us accidentally storing a reference parameter.
 //
 // The ForwardType should only be used for unbound arguments.
-template <typename T>
-struct CallbackParamTraitsForNonMoveOnlyType<T&> {
-  typedef T& ForwardType;
-  typedef T StorageType;
-};
+// template <typename T>
+// struct CallbackParamTraits<T&> {
+  // typedef T& ForwardType;
+  // typedef T StorageType;
+// };
 
 // Note that for array types, we implicitly add a const in the conversion. This
 // means that it is not possible to bind array arguments to functions that take
 // a non-const pointer. Trying to specialize the template based on a "const
 // T[n]" does not seem to match correctly, so we are stuck with this
 // restriction.
 template <typename T, size_t n>
 struct CallbackParamTraitsForNonMoveOnlyType<T[n]> {
   typedef const T* ForwardType;
   typedef const T* StorageType;
@@ skipping 14 matching lines @@
 // helper function.  When used with Bind(), this signifies transferal of the
 // object's state to the target function.
 //
 // For these types, the ForwardType must not be a const reference, or a
 // reference.  A const reference is inappropriate, and would break const
 // correctness, because we are implementing a destructive move.  A non-const
 // reference cannot be used with temporaries which means the result of a
 // function or a cast would not be usable with Callback<> or Bind().
 template <typename T>
 struct CallbackParamTraitsForMoveOnlyType {
-  typedef T ForwardType;
+  typedef typename std::remove_reference<T>::type&& ForwardType;
   typedef T StorageType;
 };
 
 // CallbackForward() is a very limited simulation of C++11's std::forward()
 // used by the Callback/Bind system for a set of movable-but-not-copyable
 // types.  It is needed because forwarding a movable-but-not-copyable
 // argument to another function requires us to invoke the proper move
 // operator to create a rvalue version of the type.  The supported types are
 // whitelisted below as overloads of the CallbackForward() function. The
 // default template compiles out to be a no-op.
 //
 // In C++11, std::forward would replace all uses of this function.  However, it
 // is impossible to implement a general std::forward with C++11 due to a lack
 // of rvalue references.
 //
 // In addition to Callback/Bind, this is used by PostTaskAndReplyWithResult to
 // simulate std::forward() and forward the result of one Callback as a
 // parameter to another callback. This is to support Callbacks that return
 // the movable-but-not-copyable types whitelisted above.
 template <typename T>
 typename enable_if<!IsMoveOnlyType<T>::value, T>::type& CallbackForward(T& t) {
   return t;
 }
 
 template <typename T>
 typename enable_if<IsMoveOnlyType<T>::value, T>::type CallbackForward(T& t) {
   return t.Pass();
 }
 
+template <typename T>
+auto CallbackForward2(T&& t) ->
+    typename CallbackParamTraits<T>::ForwardType {
+  return static_cast<typename CallbackParamTraits<T>::ForwardType>(t);
+}
+
 }  // namespace internal
 }  // namespace base
 
 #endif  // BASE_CALLBACK_INTERNAL_H_