| // Copyright 2024 The Dawn & Tint Authors | |
| // | |
| // Redistribution and use in source and binary forms, with or without | |
| // modification, are permitted provided that the following conditions are met: | |
| // | |
| // 1. Redistributions of source code must retain the above copyright notice, this | |
| // list of conditions and the following disclaimer. | |
| // | |
| // 2. Redistributions in binary form must reproduce the above copyright notice, | |
| // this list of conditions and the following disclaimer in the documentation | |
| // and/or other materials provided with the distribution. | |
| // | |
| // 3. Neither the name of the copyright holder nor the names of its | |
| // contributors may be used to endorse or promote products derived from | |
| // this software without specific prior written permission. | |
| // | |
| // THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS" | |
| // AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE | |
| // IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE | |
| // DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR CONTRIBUTORS BE LIABLE | |
| // FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL | |
| // DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR | |
| // SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER | |
| // CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, | |
| // OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE | |
| // OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE. | |
| #ifndef SRC_DAWN_COMMON_MATCHVARIANT_H_ | |
| #define SRC_DAWN_COMMON_MATCHVARIANT_H_ | |
| #include <variant> | |
| namespace dawn { | |
| // This is the `Overloaded` template in chromium/src/base/functional/Overloaded.h. | |
| // std::visit() needs to be called with a functor object, such as | |
| // | |
| // struct Visitor { | |
| // std::string operator()(const PackageA& source) { | |
| // return "PackageA"; | |
| // } | |
| // | |
| // std::string operator()(const PackageB& source) { | |
| // return "PackageB"; | |
| // } | |
| // }; | |
| // | |
| // std::variant<PackageA, PackageB> var = PackageA(); | |
| // return std::visit(Visitor(), var); | |
| // | |
| // `Overloaded` enables the above code to be written as: | |
| // | |
| // std::visit( | |
| // Overloaded{ | |
| // [](const PackageA& pack) { return "PackageA"; }, | |
| // [](const PackageB& pack) { return "PackageB"; }, | |
| // }, var); | |
| // | |
| // Note: Overloads must be implemented for all the variant options. Otherwise, there will be a | |
| // compilation error. | |
| // | |
| // This struct inherits operator() method from all its base classes. Introduces operator() method | |
| // from all its base classes into its definition. | |
| template <typename... Callables> | |
| struct Overloaded : Callables... { | |
| using Callables::operator()...; | |
| }; | |
| // Uses template argument deduction so that the `Overloaded` struct can be used without specifying | |
| // its template argument. This allows anonymous lambdas passed into the `Overloaded` constructor. | |
| template <typename... Callables> | |
| Overloaded(Callables...) -> Overloaded<Callables...>; | |
| // With this template we can simplify the call of std::visit(Overloaded{...}, variant). | |
| template <typename Variant, typename... Callables> | |
| auto MatchVariant(const Variant& v, Callables... args) { | |
| return std::visit(Overloaded{args...}, v); | |
| } | |
| } // namespace dawn | |
| #endif |