chromium/third_party/abseil-cpp/absl/functional/internal/function_ref.h

// Copyright 2019 The Abseil Authors.
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
//      https://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.

#ifndef ABSL_FUNCTIONAL_INTERNAL_FUNCTION_REF_H_
#define ABSL_FUNCTIONAL_INTERNAL_FUNCTION_REF_H_

#include <cassert>
#include <functional>
#include <type_traits>

#include "absl/base/internal/invoke.h"
#include "absl/functional/any_invocable.h"
#include "absl/meta/type_traits.h"

namespace absl {
ABSL_NAMESPACE_BEGIN
namespace functional_internal {

// Like a void* that can handle function pointers as well. The standard does not
// allow function pointers to round-trip through void*, but void(*)() is fine.
//
// Note: It's important that this class remains trivial and is the same size as
// a pointer, since this allows the compiler to perform tail-call optimizations
// when the underlying function is a callable object with a matching signature.
VoidPtr;

// Chooses the best type for passing T as an argument.
// Attempt to be close to SystemV AMD64 ABI. Objects with trivial copy ctor are
// passed by value.
template <typename T,
          bool IsLValueReference = std::is_lvalue_reference<T>::value>
struct PassByValue : std::false_type { … };

PassByValue<T, false>;

template <typename T>
struct ForwardT : std::conditional<PassByValue<T>::value, T, T&&> { … };

// An Invoker takes a pointer to the type-erased invokable object, followed by
// the arguments that the invokable object expects.
//
// Note: The order of arguments here is an optimization, since member functions
// have an implicit "this" pointer as their first argument, putting VoidPtr
// first allows the compiler to perform tail-call optimization in many cases.
Invoker;

//
// InvokeObject and InvokeFunction provide static "Invoke" functions that can be
// used as Invokers for objects or functions respectively.
//
// static_cast<R> handles the case the return type is void.
template <typename Obj, typename R, typename... Args>
R InvokeObject(VoidPtr ptr, typename ForwardT<Args>::type... args) { … }

template <typename Fun, typename R, typename... Args>
R InvokeFunction(VoidPtr ptr, typename ForwardT<Args>::type... args) { … }

template <typename Sig>
void AssertNonNull(const std::function<Sig>& f) { … }

template <typename Sig>
void AssertNonNull(const AnyInvocable<Sig>& f) { … }

template <typename F>
void AssertNonNull(const F&) { … }

template <typename F, typename C>
void AssertNonNull(F C::*f) { … }

EnableIf;

}  // namespace functional_internal
ABSL_NAMESPACE_END
}  // namespace absl

#endif  // ABSL_FUNCTIONAL_INTERNAL_FUNCTION_REF_H_