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94 lines
2.6 KiB
94 lines
2.6 KiB
// Copyright The OpenTelemetry Authors |
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// SPDX-License-Identifier: Apache-2.0 |
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#pragma once |
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#include <iosfwd> |
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#include <memory> // IWYU pragma: keep |
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#include <type_traits> |
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#include <utility> |
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#include "opentelemetry/version.h" |
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OPENTELEMETRY_BEGIN_NAMESPACE |
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namespace nostd |
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{ |
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template <class Sig> |
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class function_ref; // IWYU pragma: keep |
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/** |
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* Non-owning function reference that can be used as a more performant |
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* replacement for std::function when ownership sematics aren't needed. |
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* |
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* See http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2017/p0792r0.html |
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* |
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* Based off of https://stackoverflow.com/a/39087660/4447365 |
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*/ |
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template <class R, class... Args> |
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class function_ref<R(Args...)> |
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{ |
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void *callable_ = nullptr; |
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R (*invoker_)(void *, Args...) = nullptr; |
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template <class F> |
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using FunctionPointer = decltype(std::addressof(std::declval<F &>())); |
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template <class F> |
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void BindTo(F &f) noexcept |
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{ |
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callable_ = static_cast<void *>(std::addressof(f)); |
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invoker_ = [](void *callable, Args... args) -> R { |
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return (*static_cast<FunctionPointer<F>>(callable))(std::forward<Args>(args)...); |
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}; |
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} |
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template <class R_in, class... Args_in> |
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void BindTo(R_in (*f)(Args_in...)) noexcept |
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{ |
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using F = decltype(f); |
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if (f == nullptr) |
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{ |
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return BindTo(nullptr); |
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} |
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callable_ = reinterpret_cast<void *>(f); |
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invoker_ = [](void *callable, Args... args) -> R { |
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return (F(callable))(std::forward<Args>(args)...); |
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}; |
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} |
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void BindTo(std::nullptr_t) noexcept |
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{ |
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callable_ = nullptr; |
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invoker_ = nullptr; |
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} |
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public: |
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template < |
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class F, |
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typename std::enable_if<!std::is_same<function_ref, typename std::decay<F>::type>::value, |
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int>::type = 0, |
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typename std::enable_if< |
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#if (__cplusplus >= 201703L) || (defined(_MSVC_LANG) && (_MSVC_LANG > 201402)) |
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// std::result_of deprecated in C++17, removed in C++20 |
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std::is_convertible<typename std::invoke_result<F, Args...>::type, R>::value, |
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#else |
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// std::result_of since C++11 |
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std::is_convertible<typename std::result_of<F &(Args...)>::type, R>::value, |
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#endif |
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int>::type = 0> |
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function_ref(F &&f) |
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{ |
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BindTo(f); // not forward |
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} |
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function_ref(std::nullptr_t) {} |
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function_ref(const function_ref &) noexcept = default; |
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function_ref(function_ref &&) noexcept = default; |
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R operator()(Args... args) const { return invoker_(callable_, std::forward<Args>(args)...); } |
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explicit operator bool() const { return invoker_; } |
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}; |
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} // namespace nostd |
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OPENTELEMETRY_END_NAMESPACE
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