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()) \
29     test(int) {                                                               \
30       return true;                                                            \
31     }                                                                         \
32     template <typename V, typename W>                                         \
33     static constexpr bool test(...) {                                         \
34       return false;                                                           \
35     }                                                                         \
36     static constexpr bool value = test<T, U>(int());                          \
37   }
38 
39 DEFINE_HAS_BINARY_OP_TRAIT(has_eq_op, ==);
40 DEFINE_HAS_BINARY_OP_TRAIT(has_lt_op, <);
41 
42 /**
43  * Type trait that checks if two types can be equated (==) and compared (<).
44  */
45 template <typename T, typename U>
46 struct is_comparable {
47   static constexpr bool value =
48       has_eq_op<T, U>::value && has_lt_op<T, U>::value;
49 };
50 
51 }  // namespace aapt
52 
53 #endif /* AAPT_UTIL_TYPETRAITS_H */
54