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// Copyright 2023 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.
// The IfConstexpr and IfConstexprElse utilities in this file are meant to be
// used to emulate `if constexpr` in pre-C++17 mode in library implementation.
// The motivation is to allow for avoiding complex SFINAE.
//
// The functions passed in must depend on the type(s) of the object(s) that
// require SFINAE. For example:
// template<typename T>
// int MaybeFoo(T& t) {
// if constexpr (HasFoo<T>::value) return t.foo();
// return 0;
// }
//
// can be written in pre-C++17 as:
//
// template<typename T>
// int MaybeFoo(T& t) {
// int i = 0;
// absl::utility_internal::IfConstexpr<HasFoo<T>::value>(
// [&](const auto& fooer) { i = fooer.foo(); }, t);
// return i;
// }
#ifndef ABSL_UTILITY_INTERNAL_IF_CONSTEXPR_H_
#define ABSL_UTILITY_INTERNAL_IF_CONSTEXPR_H_
#include <tuple>
#include <utility>
#include "absl/base/config.h"
namespace absl {
ABSL_NAMESPACE_BEGIN
namespace utility_internal {
template <bool condition, typename TrueFunc, typename FalseFunc,
typename... Args>
auto IfConstexprElse(TrueFunc&& true_func, FalseFunc&& false_func,
Args&&... args) {
return std::get<condition>(std::forward_as_tuple(
std::forward<FalseFunc>(false_func), std::forward<TrueFunc>(true_func)))(
std::forward<Args>(args)...);
}
template <bool condition, typename Func, typename... Args>
void IfConstexpr(Func&& func, Args&&... args) {
IfConstexprElse<condition>(std::forward<Func>(func), [](auto&&...){},
std::forward<Args>(args)...);
}
} // namespace utility_internal
ABSL_NAMESPACE_END
} // namespace absl
#endif // ABSL_UTILITY_INTERNAL_IF_CONSTEXPR_H_
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