Support nested OnceCallback on Callback::IsCancelled

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 393 matching lines @@
     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 BindStateType>
+struct CallbackCancellationChecker {
+  static constexpr bool is_cancellable = true;
+  static bool Run(const BindStateBase* base) {
+    return static_cast<const BindStateType*>(base)->functor_.IsCancelled();
+  }
+};
+
 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();
-  }
-};
+struct CancellationChecker<BindState<OnceCallback<Signature>, BoundArgs...>>
+    : CallbackCancellationChecker<
+          BindState<OnceCallback<Signature>, BoundArgs...>> {};
+
+template <typename Signature, typename... BoundArgs>
+struct CancellationChecker<
+    BindState<RepeatingCallback<Signature>, BoundArgs...>>
+    : CallbackCancellationChecker<
+          BindState<RepeatingCallback<Signature>, BoundArgs...>> {};
 
 // 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>
@@ skipping 89 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_