1 // Copyright 2021 gRPC authors. 2 // 3 // Licensed under the Apache License, Version 2.0 (the "License"); 4 // you may not use this file except in compliance with the License. 5 // You may obtain a copy of the License at 6 // 7 // http://www.apache.org/licenses/LICENSE-2.0 8 // 9 // Unless required by applicable law or agreed to in writing, software 10 // distributed under the License is distributed on an "AS IS" BASIS, 11 // WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. 12 // See the License for the specific language governing permissions and 13 // limitations under the License. 14 15 #ifndef GRPC_SRC_CORE_LIB_GPRPP_MATCH_H 16 #define GRPC_SRC_CORE_LIB_GPRPP_MATCH_H 17 18 #include <grpc/support/port_platform.h> 19 20 #include <utility> 21 22 #include "absl/types/variant.h" 23 24 #include "src/core/lib/gprpp/overload.h" 25 26 namespace grpc_core { 27 28 namespace detail { 29 30 template <typename... Cases> 31 struct MatchPointerExtractor { 32 OverloadType<Cases...> cases; 33 template <typename T> 34 auto operator()(T& value) -> decltype(cases(&value)) { 35 return cases(&value); 36 } 37 }; 38 39 } // namespace detail 40 41 /// Match on a variant. 42 /// Given variant \a value, and a set of callables \a fs, call the appropriate 43 /// callable based on the type contained in \a value. 44 /// 45 /// Example (prints "hoorah"): 46 /// variant<int, string> v = 42; 47 /// Match(v, 48 /// [](int i) { puts("hoorah"); }, 49 /// [](string s) { puts("boo"); }); 50 template <typename... Fs, typename T0, typename... Ts> 51 auto Match(const absl::variant<T0, Ts...>& value, Fs... fs) 52 -> decltype(std::declval<OverloadType<Fs...>>()(std::declval<T0>())) { 53 return absl::visit(Overload(std::move(fs)...), value); 54 } 55 56 /// A version of Match that takes a mutable pointer to a variant and calls its 57 /// overload callables with a mutable pointer to the current variant value. 58 /// 59 /// Example: 60 /// variant<int, string> v = 42; 61 /// MatchMutable(&v, 62 /// [](int* i) { *i = 1; }, 63 /// [](string* s) { *s = "foo"; }); 64 /// // v now contains 1. 65 template <typename... Fs, typename T0, typename... Ts> 66 auto MatchMutable(absl::variant<T0, Ts...>* value, Fs... fs) 67 -> decltype(std::declval<OverloadType<Fs...>>()(std::declval<T0*>())) { 68 return absl::visit(detail::MatchPointerExtractor<Fs...>{OverloadType<Fs...>( 69 std::move(fs)...)}, 70 *value); 71 } 72 73 } // namespace grpc_core 74 75 #endif // GRPC_SRC_CORE_LIB_GPRPP_MATCH_H 76