Split BindStateBase ctor for non-cancellable Bind

base/bind_internal.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.
 
 #ifndef BASE_BIND_INTERNAL_H_
 #define BASE_BIND_INTERNAL_H_
 
 #include <stddef.h>
 
 #include <tuple>
@@ skipping 360 matching lines @@
 typename std::enable_if<!FunctorTraits<Functor>::is_nullable, bool>::type
 IsNull(const Functor&) {
   return false;
 }
 
 template <typename Functor, typename... BoundArgs>
 struct BindState;
 
 template <typename BindStateType, typename SFINAE = void>
 struct CancellationChecker {
+  static constexpr bool is_cancellable = false;
   static bool Run(const BindStateBase*) {
     return false;
   }
 };
 
 template <typename Functor, typename... BoundArgs>
 struct CancellationChecker<
     BindState<Functor, BoundArgs...>,
     typename std::enable_if<IsWeakMethod<FunctorTraits<Functor>::is_method,
                                          BoundArgs...>::value>::type> {
+  static constexpr bool is_cancellable = true;
   static bool Run(const BindStateBase* base) {
     using BindStateType = BindState<Functor, BoundArgs...>;
     const BindStateType* bind_state = static_cast<const BindStateType*>(base);
     return !base::get<0>(bind_state->bound_args_);
   }
 };
 
 template <typename Signature, typename... BoundArgs>
 struct CancellationChecker<BindState<Callback<Signature>, BoundArgs...>> {
+  static constexpr bool is_cancellable = true;
   static bool Run(const BindStateBase* base) {
     using Functor = Callback<Signature>;
     using BindStateType = BindState<Functor, BoundArgs...>;
     const BindStateType* bind_state = static_cast<const BindStateType*>(base);
     return bind_state->functor_.IsCancelled();
   }
 };
 
 // BindState<>
 //
 // This stores all the state passed into Bind().
 template <typename Functor, typename... BoundArgs>
 struct BindState final : BindStateBase {
+  using IsCancellable = std::integral_constant<
+      bool, CancellationChecker<BindState>::is_cancellable>;
+
   template <typename ForwardFunctor, typename... ForwardBoundArgs>
   explicit BindState(BindStateBase::InvokeFuncStorage invoke_func,
                      ForwardFunctor&& functor,
                      ForwardBoundArgs&&... bound_args)
+      : BindState(IsCancellable(),

[dcheng, 2016/09/09 20:39:01]

Is this a C++14ism? How does it work with our toolchain? =)

[dcheng, 2016/09/09 20:39:27]

Also, see
https://github.com/llvm-mirror/libcxx/blob/master/include/type_traits#L505

+                  invoke_func,
+                  std::forward<ForwardFunctor>(functor),
+                  std::forward<ForwardBoundArgs>(bound_args)...) {}
+
+  Functor functor_;
+  std::tuple<BoundArgs...> bound_args_;
+
+ private:
+  template <typename ForwardFunctor, typename... ForwardBoundArgs>
+  explicit BindState(std::true_type,
+                     BindStateBase::InvokeFuncStorage invoke_func,
+                     ForwardFunctor&& functor,
+                     ForwardBoundArgs&&... bound_args)
       : BindStateBase(invoke_func, &Destroy,
                       &CancellationChecker<BindState>::Run),
         functor_(std::forward<ForwardFunctor>(functor)),
         bound_args_(std::forward<ForwardBoundArgs>(bound_args)...) {
     DCHECK(!IsNull(functor_));
   }
 
-  Functor functor_;
-  std::tuple<BoundArgs...> bound_args_;
+  template <typename ForwardFunctor, typename... ForwardBoundArgs>
+  explicit BindState(std::false_type,
+                     BindStateBase::InvokeFuncStorage invoke_func,
+                     ForwardFunctor&& functor,
+                     ForwardBoundArgs&&... bound_args)
+      : BindStateBase(invoke_func, &Destroy),
+        functor_(std::forward<ForwardFunctor>(functor)),
+        bound_args_(std::forward<ForwardBoundArgs>(bound_args)...) {
+    DCHECK(!IsNull(functor_));
+  }
 
- private:
   ~BindState() {}
 
   static void Destroy(BindStateBase* self) {
     delete static_cast<BindState*>(self);
   }
 };
 
 // Used to implement MakeBindStateType.
 template <bool is_method, typename Functor, typename... BoundArgs>
 struct MakeBindStateTypeImpl;
@@ skipping 42 matching lines @@
 
 // Returns a RunType of bound functor.
 // E.g. MakeUnboundRunType<R(A, B, C), A, B> is evaluated to R(C).
 template <typename Functor, typename... BoundArgs>
 using MakeUnboundRunType =
     typename internal::MakeUnboundRunTypeImpl<Functor, BoundArgs...>::Type;
 
 }  // namespace base
 
 #endif  // BASE_BIND_INTERNAL_H_