mirror of
https://github.com/abseil/abseil-cpp.git
synced 2026-06-04 20:14:23 +08:00
74 lines
2.1 KiB
C++
74 lines
2.1 KiB
C++
// Copyright 2025 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_META_INTERNAL_CONSTEXPR_TESTING_H_
|
|
#define ABSL_META_INTERNAL_CONSTEXPR_TESTING_H_
|
|
|
|
#include <type_traits>
|
|
|
|
#include "absl/base/config.h"
|
|
|
|
namespace absl {
|
|
ABSL_NAMESPACE_BEGIN
|
|
namespace meta_internal {
|
|
|
|
// HasConstexprEvaluation([] { ... }) will evaluate to `true` if the
|
|
// lambda can be evaluated in a constant expression and `false`
|
|
// otherwise.
|
|
// The return type of the lambda is not relevant, as long as the whole
|
|
// evaluation works in a constant expression.
|
|
template <typename F>
|
|
constexpr bool HasConstexprEvaluation(F f);
|
|
|
|
/// Implementation details below ///
|
|
|
|
namespace internal_constexpr_evaluation {
|
|
|
|
#ifdef __clang__
|
|
#pragma clang diagnostic push
|
|
#pragma clang diagnostic ignored "-Wuninitialized"
|
|
#endif
|
|
// This will give a constexpr instance of `F`.
|
|
// This works for captureless lambdas because they have no state and the copy
|
|
// constructor does not look at the input reference.
|
|
template <typename F>
|
|
constexpr F default_instance = default_instance<F>;
|
|
#ifdef __clang__
|
|
#pragma clang diagnostic pop
|
|
#endif
|
|
|
|
template <typename F>
|
|
constexpr std::integral_constant<bool, (default_instance<F>(), true)> Tester(
|
|
int) {
|
|
return {};
|
|
}
|
|
|
|
template <typename S>
|
|
constexpr std::false_type Tester(char) {
|
|
return {};
|
|
}
|
|
|
|
} // namespace internal_constexpr_evaluation
|
|
|
|
template <typename F>
|
|
constexpr bool HasConstexprEvaluation(F) {
|
|
return internal_constexpr_evaluation::Tester<F>(0);
|
|
}
|
|
|
|
} // namespace meta_internal
|
|
ABSL_NAMESPACE_END
|
|
} // namespace absl
|
|
|
|
#endif // ABSL_META_INTERNAL_CONSTEXPR_TESTING_H_
|