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