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- /*
- * Copyright 2017-present Facebook, Inc.
- *
- * 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
- *
- * http://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.
- */
- #pragma once
- #include <type_traits>
- #include <utility>
- /**
- * folly implementation of `std::overload` like functionality
- *
- * Example:
- * struct One {};
- * struct Two {};
- * boost::variant<One, Two> value;
- *
- * variant_match(value,
- * [] (const One& one) { ... },
- * [] (const Two& two) { ... });
- */
- namespace folly {
- namespace detail {
- template <typename...>
- struct Overload;
- template <typename Case, typename... Cases>
- struct Overload<Case, Cases...> : Overload<Cases...>, Case {
- Overload(Case c, Cases... cs)
- : Overload<Cases...>(std::move(cs)...), Case(std::move(c)) {}
- using Case::operator();
- using Overload<Cases...>::operator();
- };
- template <typename Case>
- struct Overload<Case> : Case {
- explicit Overload(Case c) : Case(std::move(c)) {}
- using Case::operator();
- };
- } // namespace detail
- /*
- * Combine multiple `Cases` in one function object
- */
- template <typename... Cases>
- decltype(auto) overload(Cases&&... cases) {
- return detail::Overload<typename std::decay<Cases>::type...>{
- std::forward<Cases>(cases)...};
- }
- /*
- * Match `Variant` with one of the `Cases`
- *
- * Note: you can also use `[] (const auto&) {...}` as default case
- *
- */
- template <typename Variant, typename... Cases>
- decltype(auto) variant_match(Variant&& variant, Cases&&... cases) {
- return apply_visitor(
- overload(std::forward<Cases>(cases)...), std::forward<Variant>(variant));
- }
- } // namespace folly
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