1 /* 2 * Copyright (C) 2015 The Android Open Source Project 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 * http://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 AAPT_UTIL_TYPETRAITS_H 18 #define AAPT_UTIL_TYPETRAITS_H 19 20 #include <type_traits> 21 22 namespace aapt { 23 24 #define DEFINE_HAS_BINARY_OP_TRAIT(name, op) \ 25 template <typename T, typename U> \ 26 struct name { \ 27 template <typename V, typename W> \ 28 static constexpr decltype(std::declval<V>() op std::declval<W>(), bool()) test(int) { \ 29 return true; \ 30 } \ 31 template <typename V, typename W> \ 32 static constexpr bool test(...) { \ 33 return false; \ 34 } \ 35 static constexpr bool value = test<T, U>(int()); \ 36 } 37 38 DEFINE_HAS_BINARY_OP_TRAIT(has_eq_op, ==); 39 DEFINE_HAS_BINARY_OP_TRAIT(has_lt_op, <); 40 41 /** 42 * Type trait that checks if two types can be equated (==) and compared (<). 43 */ 44 template <typename T, typename U> 45 struct is_comparable { 46 static constexpr bool value = has_eq_op<T, U>::value && has_lt_op<T, U>::value; 47 }; 48 49 } // namespace aapt 50 51 #endif /* AAPT_UTIL_TYPETRAITS_H */ 52