1// Copyright 2018 The Amber 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 SRC_CAST_HASH_H_
16#define SRC_CAST_HASH_H_
17
18#include <cstddef>
19
20namespace amber {
21
22/// A hash implementation for types that can trivially be up-cast to a size_t.
23/// For example, use this as a hasher for an enum whose underlying type is
24/// an integer no wider than size_t.
25///
26/// The need for this was a defect in the C++11 library, and has been fixed
27/// in C++14.  http://www.open-std.org/jtc1/sc22/wg21/docs/lwg-defects.html#2148
28template <typename T>
29struct CastHash {
30  size_t operator()(const T& value) const { return static_cast<size_t>(value); }
31};
32
33}  // namespace amber
34
35#endif  // SRC_CAST_HASH_H_
36