Abseil Common Libraries (C++) (grcp 依赖)
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106 lines
3.6 KiB
106 lines
3.6 KiB
// Copyright 2019 The Abseil Authors. |
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// |
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// Licensed under the Apache License, Version 2.0 (the "License"); |
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// you may not use this file except in compliance with the License. |
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// You may obtain a copy of the License at |
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// |
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// https://www.apache.org/licenses/LICENSE-2.0 |
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// |
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// Unless required by applicable law or agreed to in writing, software |
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// distributed under the License is distributed on an "AS IS" BASIS, |
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// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. |
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// See the License for the specific language governing permissions and |
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// limitations under the License. |
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#ifndef ABSL_FUNCTIONAL_INTERNAL_FUNCTION_REF_H_ |
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#define ABSL_FUNCTIONAL_INTERNAL_FUNCTION_REF_H_ |
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#include <cassert> |
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#include <functional> |
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#include <type_traits> |
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#include "absl/base/internal/invoke.h" |
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#include "absl/meta/type_traits.h" |
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namespace absl { |
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ABSL_NAMESPACE_BEGIN |
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namespace functional_internal { |
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// Like a void* that can handle function pointers as well. The standard does not |
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// allow function pointers to round-trip through void*, but void(*)() is fine. |
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// |
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// Note: It's important that this class remains trivial and is the same size as |
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// a pointer, since this allows the compiler to perform tail-call optimizations |
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// when the underlying function is a callable object with a matching signature. |
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union VoidPtr { |
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const void* obj; |
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void (*fun)(); |
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}; |
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// Chooses the best type for passing T as an argument. |
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// Attempt to be close to SystemV AMD64 ABI. Objects with trivial copy ctor are |
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// passed by value. |
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template <typename T> |
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constexpr bool PassByValue() { |
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return !std::is_lvalue_reference<T>::value && |
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absl::is_trivially_copy_constructible<T>::value && |
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absl::is_trivially_copy_assignable< |
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typename std::remove_cv<T>::type>::value && |
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std::is_trivially_destructible<T>::value && |
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sizeof(T) <= 2 * sizeof(void*); |
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} |
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template <typename T> |
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struct ForwardT : std::conditional<PassByValue<T>(), T, T&&> {}; |
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// An Invoker takes a pointer to the type-erased invokable object, followed by |
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// the arguments that the invokable object expects. |
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// |
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// Note: The order of arguments here is an optimization, since member functions |
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// have an implicit "this" pointer as their first argument, putting VoidPtr |
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// first allows the compiler to perform tail-call optimization in many cases. |
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template <typename R, typename... Args> |
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using Invoker = R (*)(VoidPtr, typename ForwardT<Args>::type...); |
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// |
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// InvokeObject and InvokeFunction provide static "Invoke" functions that can be |
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// used as Invokers for objects or functions respectively. |
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// |
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// static_cast<R> handles the case the return type is void. |
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template <typename Obj, typename R, typename... Args> |
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R InvokeObject(VoidPtr ptr, typename ForwardT<Args>::type... args) { |
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auto o = static_cast<const Obj*>(ptr.obj); |
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return static_cast<R>( |
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absl::base_internal::Invoke(*o, std::forward<Args>(args)...)); |
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} |
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template <typename Fun, typename R, typename... Args> |
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R InvokeFunction(VoidPtr ptr, typename ForwardT<Args>::type... args) { |
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auto f = reinterpret_cast<Fun>(ptr.fun); |
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return static_cast<R>( |
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absl::base_internal::Invoke(f, std::forward<Args>(args)...)); |
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} |
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template <typename Sig> |
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void AssertNonNull(const std::function<Sig>& f) { |
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assert(f != nullptr); |
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(void)f; |
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} |
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template <typename F> |
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void AssertNonNull(const F&) {} |
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template <typename F, typename C> |
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void AssertNonNull(F C::*f) { |
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assert(f != nullptr); |
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(void)f; |
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} |
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template <bool C> |
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using EnableIf = typename ::std::enable_if<C, int>::type; |
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} // namespace functional_internal |
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ABSL_NAMESPACE_END |
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} // namespace absl |
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#endif // ABSL_FUNCTIONAL_INTERNAL_FUNCTION_REF_H_
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