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266 lines
10 KiB
C++
266 lines
10 KiB
C++
// Copyright (c) 2011 The Chromium Authors. All rights reserved.
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// Use of this source code is governed by a BSD-style license that can be
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// found in the LICENSE file.
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#ifndef BASE_BIND_H_
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#define BASE_BIND_H_
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#include <utility>
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#include "base/bind_internal.h"
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// -----------------------------------------------------------------------------
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// Usage documentation
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// -----------------------------------------------------------------------------
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//
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// See //docs/callback.md for documentation.
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//
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//
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// -----------------------------------------------------------------------------
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// Implementation notes
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// -----------------------------------------------------------------------------
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//
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// If you're reading the implementation, before proceeding further, you should
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// read the top comment of base/bind_internal.h for a definition of common
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// terms and concepts.
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namespace base {
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namespace internal {
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// IsOnceCallback<T> is a std::true_type if |T| is a OnceCallback.
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template <typename T>
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struct IsOnceCallback : std::false_type {};
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template <typename Signature>
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struct IsOnceCallback<OnceCallback<Signature>> : std::true_type {};
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// Helper to assert that parameter |i| of type |Arg| can be bound, which means:
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// - |Arg| can be retained internally as |Storage|.
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// - |Arg| can be forwarded as |Unwrapped| to |Param|.
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template <size_t i,
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typename Arg,
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typename Storage,
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typename Unwrapped,
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typename Param>
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struct AssertConstructible {
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private:
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static constexpr bool param_is_forwardable =
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std::is_constructible<Param, Unwrapped>::value;
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// Unlike the check for binding into storage below, the check for
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// forwardability drops the const qualifier for repeating callbacks. This is
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// to try to catch instances where std::move()--which forwards as a const
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// reference with repeating callbacks--is used instead of base::Passed().
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static_assert(
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param_is_forwardable ||
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!std::is_constructible<Param, std::decay_t<Unwrapped>&&>::value,
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"Bound argument |i| is move-only but will be forwarded by copy. "
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"Ensure |Arg| is bound using base::Passed(), not std::move().");
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static_assert(
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param_is_forwardable,
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"Bound argument |i| of type |Arg| cannot be forwarded as "
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"|Unwrapped| to the bound functor, which declares it as |Param|.");
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static constexpr bool arg_is_storable =
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std::is_constructible<Storage, Arg>::value;
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static_assert(arg_is_storable ||
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!std::is_constructible<Storage, std::decay_t<Arg>&&>::value,
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"Bound argument |i| is move-only but will be bound by copy. "
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"Ensure |Arg| is mutable and bound using std::move().");
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static_assert(arg_is_storable,
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"Bound argument |i| of type |Arg| cannot be converted and "
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"bound as |Storage|.");
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};
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// Takes three same-length TypeLists, and applies AssertConstructible for each
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// triples.
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template <typename Index,
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typename Args,
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typename UnwrappedTypeList,
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typename ParamsList>
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struct AssertBindArgsValidity;
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template <size_t... Ns,
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typename... Args,
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typename... Unwrapped,
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typename... Params>
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struct AssertBindArgsValidity<std::index_sequence<Ns...>,
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TypeList<Args...>,
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TypeList<Unwrapped...>,
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TypeList<Params...>>
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: AssertConstructible<Ns, Args, std::decay_t<Args>, Unwrapped, Params>... {
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static constexpr bool ok = true;
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};
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// The implementation of TransformToUnwrappedType below.
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template <bool is_once, typename T>
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struct TransformToUnwrappedTypeImpl;
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template <typename T>
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struct TransformToUnwrappedTypeImpl<true, T> {
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using StoredType = std::decay_t<T>;
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using ForwardType = StoredType&&;
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using Unwrapped = decltype(Unwrap(std::declval<ForwardType>()));
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};
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template <typename T>
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struct TransformToUnwrappedTypeImpl<false, T> {
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using StoredType = std::decay_t<T>;
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using ForwardType = const StoredType&;
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using Unwrapped = decltype(Unwrap(std::declval<ForwardType>()));
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};
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// Transform |T| into `Unwrapped` type, which is passed to the target function.
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// Example:
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// In is_once == true case,
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// `int&&` -> `int&&`,
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// `const int&` -> `int&&`,
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// `OwnedWrapper<int>&` -> `int*&&`.
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// In is_once == false case,
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// `int&&` -> `const int&`,
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// `const int&` -> `const int&`,
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// `OwnedWrapper<int>&` -> `int* const &`.
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template <bool is_once, typename T>
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using TransformToUnwrappedType =
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typename TransformToUnwrappedTypeImpl<is_once, T>::Unwrapped;
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// Transforms |Args| into `Unwrapped` types, and packs them into a TypeList.
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// If |is_method| is true, tries to dereference the first argument to support
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// smart pointers.
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template <bool is_once, bool is_method, typename... Args>
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struct MakeUnwrappedTypeListImpl {
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using Type = TypeList<TransformToUnwrappedType<is_once, Args>...>;
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};
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// Performs special handling for this pointers.
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// Example:
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// int* -> int*,
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// std::unique_ptr<int> -> int*.
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template <bool is_once, typename Receiver, typename... Args>
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struct MakeUnwrappedTypeListImpl<is_once, true, Receiver, Args...> {
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using UnwrappedReceiver = TransformToUnwrappedType<is_once, Receiver>;
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using Type = TypeList<decltype(&*std::declval<UnwrappedReceiver>()),
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TransformToUnwrappedType<is_once, Args>...>;
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};
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template <bool is_once, bool is_method, typename... Args>
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using MakeUnwrappedTypeList =
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typename MakeUnwrappedTypeListImpl<is_once, is_method, Args...>::Type;
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} // namespace internal
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// Bind as OnceCallback.
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template <typename Functor, typename... Args>
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inline OnceCallback<MakeUnboundRunType<Functor, Args...>>
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BindOnce(Functor&& functor, Args&&... args) {
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static_assert(!internal::IsOnceCallback<std::decay_t<Functor>>() ||
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(std::is_rvalue_reference<Functor&&>() &&
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!std::is_const<std::remove_reference_t<Functor>>()),
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"BindOnce requires non-const rvalue for OnceCallback binding."
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" I.e.: base::BindOnce(std::move(callback)).");
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// This block checks if each |args| matches to the corresponding params of the
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// target function. This check does not affect the behavior of Bind, but its
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// error message should be more readable.
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using Helper = internal::BindTypeHelper<Functor, Args...>;
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using FunctorTraits = typename Helper::FunctorTraits;
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using BoundArgsList = typename Helper::BoundArgsList;
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using UnwrappedArgsList =
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internal::MakeUnwrappedTypeList<true, FunctorTraits::is_method,
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Args&&...>;
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using BoundParamsList = typename Helper::BoundParamsList;
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static_assert(internal::AssertBindArgsValidity<
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std::make_index_sequence<Helper::num_bounds>, BoundArgsList,
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UnwrappedArgsList, BoundParamsList>::ok,
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"The bound args need to be convertible to the target params.");
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using BindState = internal::MakeBindStateType<Functor, Args...>;
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using UnboundRunType = MakeUnboundRunType<Functor, Args...>;
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using Invoker = internal::Invoker<BindState, UnboundRunType>;
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using CallbackType = OnceCallback<UnboundRunType>;
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// Store the invoke func into PolymorphicInvoke before casting it to
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// InvokeFuncStorage, so that we can ensure its type matches to
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// PolymorphicInvoke, to which CallbackType will cast back.
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using PolymorphicInvoke = typename CallbackType::PolymorphicInvoke;
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PolymorphicInvoke invoke_func = &Invoker::RunOnce;
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using InvokeFuncStorage = internal::BindStateBase::InvokeFuncStorage;
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return CallbackType(new BindState(
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reinterpret_cast<InvokeFuncStorage>(invoke_func),
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std::forward<Functor>(functor),
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std::forward<Args>(args)...));
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}
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// Bind as RepeatingCallback.
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template <typename Functor, typename... Args>
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inline RepeatingCallback<MakeUnboundRunType<Functor, Args...>>
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BindRepeating(Functor&& functor, Args&&... args) {
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static_assert(
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!internal::IsOnceCallback<std::decay_t<Functor>>(),
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"BindRepeating cannot bind OnceCallback. Use BindOnce with std::move().");
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// This block checks if each |args| matches to the corresponding params of the
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// target function. This check does not affect the behavior of Bind, but its
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// error message should be more readable.
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using Helper = internal::BindTypeHelper<Functor, Args...>;
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using FunctorTraits = typename Helper::FunctorTraits;
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using BoundArgsList = typename Helper::BoundArgsList;
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using UnwrappedArgsList =
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internal::MakeUnwrappedTypeList<false, FunctorTraits::is_method,
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Args&&...>;
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using BoundParamsList = typename Helper::BoundParamsList;
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static_assert(internal::AssertBindArgsValidity<
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std::make_index_sequence<Helper::num_bounds>, BoundArgsList,
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UnwrappedArgsList, BoundParamsList>::ok,
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"The bound args need to be convertible to the target params.");
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using BindState = internal::MakeBindStateType<Functor, Args...>;
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using UnboundRunType = MakeUnboundRunType<Functor, Args...>;
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using Invoker = internal::Invoker<BindState, UnboundRunType>;
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using CallbackType = RepeatingCallback<UnboundRunType>;
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// Store the invoke func into PolymorphicInvoke before casting it to
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// InvokeFuncStorage, so that we can ensure its type matches to
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// PolymorphicInvoke, to which CallbackType will cast back.
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using PolymorphicInvoke = typename CallbackType::PolymorphicInvoke;
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PolymorphicInvoke invoke_func = &Invoker::Run;
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using InvokeFuncStorage = internal::BindStateBase::InvokeFuncStorage;
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return CallbackType(new BindState(
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reinterpret_cast<InvokeFuncStorage>(invoke_func),
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std::forward<Functor>(functor),
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std::forward<Args>(args)...));
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}
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// Unannotated Bind.
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// TODO(tzik): Deprecate this and migrate to OnceCallback and
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// RepeatingCallback, once they get ready.
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template <typename Functor, typename... Args>
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inline Callback<MakeUnboundRunType<Functor, Args...>>
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Bind(Functor&& functor, Args&&... args) {
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return BindRepeating(std::forward<Functor>(functor),
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std::forward<Args>(args)...);
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}
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// Special cases for binding to a base::Callback without extra bound arguments.
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template <typename Signature>
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OnceCallback<Signature> BindOnce(OnceCallback<Signature> closure) {
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return closure;
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}
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template <typename Signature>
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RepeatingCallback<Signature> BindRepeating(
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RepeatingCallback<Signature> closure) {
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return closure;
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}
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template <typename Signature>
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Callback<Signature> Bind(Callback<Signature> closure) {
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return closure;
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}
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} // namespace base
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#endif // BASE_BIND_H_
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