63 lines
2.3 KiB
C++
63 lines
2.3 KiB
C++
/*
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* Copyright 2022 The Android Open Source Project
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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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* http://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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*/
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#pragma once
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#include <utility>
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#include <variant>
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#include <ftl/details/match.h>
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namespace android::ftl {
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// Concise alternative to std::visit that compiles to branches rather than a dispatch table. For
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// std::variant<T0, ..., TN> where N is small, this is slightly faster since the branches can be
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// inlined unlike the function pointers.
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//
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// using namespace std::chrono;
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// std::variant<seconds, minutes, hours> duration = 119min;
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//
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// // Mutable match.
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// ftl::match(duration, [](auto& d) { ++d; });
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//
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// // Immutable match. Exhaustive due to minutes being convertible to seconds.
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// assert("2 hours"s ==
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// ftl::match(duration,
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// [](const seconds& s) {
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// const auto h = duration_cast<hours>(s);
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// return std::to_string(h.count()) + " hours"s;
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// },
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// [](const hours& h) { return std::to_string(h.count() / 24) + " days"s; }));
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//
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template <typename... Ts, typename... Ms>
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decltype(auto) match(std::variant<Ts...>& variant, Ms&&... matchers) {
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const auto matcher = details::Matcher{std::forward<Ms>(matchers)...};
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static_assert(details::is_exhaustive_match_v<decltype(matcher), Ts&...>, "Non-exhaustive match");
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return details::Match<Ts...>::match(variant, matcher);
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}
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template <typename... Ts, typename... Ms>
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decltype(auto) match(const std::variant<Ts...>& variant, Ms&&... matchers) {
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const auto matcher = details::Matcher{std::forward<Ms>(matchers)...};
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static_assert(details::is_exhaustive_match_v<decltype(matcher), const Ts&...>,
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"Non-exhaustive match");
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return details::Match<Ts...>::match(variant, matcher);
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}
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} // namespace android::ftl
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