1 // 2 // Copyright 2020 The Abseil Authors. 3 // 4 // Licensed under the Apache License, Version 2.0 (the "License"); 5 // you may not use this file except in compliance with the License. 6 // You may obtain a copy of the License at 7 // 8 // https://www.apache.org/licenses/LICENSE-2.0 9 // 10 // Unless required by applicable law or agreed to in writing, software 11 // distributed under the License is distributed on an "AS IS" BASIS, 12 // WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. 13 // See the License for the specific language governing permissions and 14 // limitations under the License. 15 // 16 17 #ifndef ABSL_BASE_INTERNAL_FAST_TYPE_ID_H_ 18 #define ABSL_BASE_INTERNAL_FAST_TYPE_ID_H_ 19 20 #include "absl/base/config.h" 21 22 namespace absl { 23 ABSL_NAMESPACE_BEGIN 24 namespace base_internal { 25 26 template <typename Type> 27 struct FastTypeTag { 28 constexpr static char dummy_var = 0; 29 }; 30 31 template <typename Type> 32 constexpr char FastTypeTag<Type>::dummy_var; 33 34 // FastTypeId<Type>() evaluates at compile/link-time to a unique pointer for the 35 // passed-in type. These are meant to be good match for keys into maps or 36 // straight up comparisons. 37 using FastTypeIdType = const void*; 38 39 template <typename Type> FastTypeId()40constexpr inline FastTypeIdType FastTypeId() { 41 return &FastTypeTag<Type>::dummy_var; 42 } 43 44 } // namespace base_internal 45 ABSL_NAMESPACE_END 46 } // namespace absl 47 48 #endif // ABSL_BASE_INTERNAL_FAST_TYPE_ID_H_ 49