| // 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 |
