Decouple Invoker from BindState

base/bind_helpers.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.
 
 // This defines a set of argument wrappers and related factory methods that
 // can be used specify the refcounting and reference semantics of arguments
 // that are bound by the Bind() function in base/bind.h.
 //
 // It also defines a set of simple functions and utilities that people want
 // when using Callback<> and Bind().
@@ skipping 444 matching lines @@
   return o.Take();
 }
 
 // IsWeakMethod is a helper that determine if we are binding a WeakPtr<> to a
 // method.  It is used internally by Bind() to select the correct
 // InvokeHelper that will no-op itself in the event the WeakPtr<> for
 // the target object is invalidated.
 //
 // The first argument should be the type of the object that will be received by
 // the method.
-template <bool IsMethod, typename... Args>
+template <bool is_method, typename... Args>
 struct IsWeakMethod : std::false_type {};
 
 template <typename T, typename... Args>
 struct IsWeakMethod<true, T, Args...> : IsWeakReceiver<T> {};
 
 // Packs a list of types to hold them in a single type.
 template <typename... Types>
 struct TypeList {};
 
 // Used for DropTypeListItem implementation.
@@ skipping 66 matching lines @@
   // MSVC 2013 doesn't support Type Alias of function types.
   // Revisit this after we update it to newer version.
   typedef R Type(Args...);
 };
 
 // A type-level function that constructs a function type that has |R| as its
 // return type and has TypeLists items as its arguments.
 template <typename R, typename ArgList>
 using MakeFunctionType = typename MakeFunctionTypeImpl<R, ArgList>::Type;
 
-// Used for ExtractArgs.
+// Used for ExtractArgs and ExtractReturnType.
 template <typename Signature>
 struct ExtractArgsImpl;
 
 template <typename R, typename... Args>
 struct ExtractArgsImpl<R(Args...)> {
-  using Type = TypeList<Args...>;
+  using ReturnType = R;
+  using ArgsList = TypeList<Args...>;
 };
 
 // A type-level function that extracts function arguments into a TypeList.
 // E.g. ExtractArgs<R(A, B, C)> is evaluated to TypeList<A, B, C>.
 template <typename Signature>
-using ExtractArgs = typename ExtractArgsImpl<Signature>::Type;
+using ExtractArgs = typename ExtractArgsImpl<Signature>::ArgsList;
+
+// A type-level function that extracts the return type of a function.
+// E.g. ExtractReturnType<R(A, B, C)> is evaluated to R.
+template <typename Signature>
+using ExtractReturnType = typename ExtractArgsImpl<Signature>::ReturnType;
 
 }  // namespace internal
 
 template <typename T>
 static inline internal::UnretainedWrapper<T> Unretained(T* o) {
   return internal::UnretainedWrapper<T>(o);
 }
 
 template <typename T>
 static inline internal::RetainedRefWrapper<T> RetainedRef(T* o) {
@@ skipping 67 matching lines @@
 
 template <typename T>
 struct IsWeakReceiver<internal::ConstRefWrapper<T>> : IsWeakReceiver<T> {};
 
 template <typename T>
 struct IsWeakReceiver<WeakPtr<T>> : std::true_type {};
 
 }  // namespace base
 
 #endif  // BASE_BIND_HELPERS_H_