1 | /* |
2 | * Copyright (c) Facebook, Inc. and its affiliates. |
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 | #pragma once |
18 | |
19 | #include <cstddef> |
20 | #include <type_traits> |
21 | |
22 | namespace folly { |
23 | namespace detail { |
24 | |
25 | // Shortcut, so we don't have to use enable_if everywhere |
26 | struct FormatTraitsBase { |
27 | typedef void enabled; |
28 | }; |
29 | |
30 | // Traits that define enabled, value_type, and at() for anything |
31 | // indexable with integral keys: pointers, arrays, vectors, and maps |
32 | // with integral keys |
33 | template <class T, class Enable = void> |
34 | struct IndexableTraits; |
35 | |
36 | // Base class for sequences (vectors, deques) |
37 | template <class C> |
38 | struct IndexableTraitsSeq : public FormatTraitsBase { |
39 | typedef C container_type; |
40 | typedef typename C::value_type value_type; |
41 | |
42 | static const value_type& at(const C& c, int idx) { |
43 | return c.at(idx); |
44 | } |
45 | |
46 | static const value_type& at(const C& c, int idx, const value_type& dflt) { |
47 | return (idx >= 0 && size_t(idx) < c.size()) ? c.at(idx) : dflt; |
48 | } |
49 | }; |
50 | |
51 | // Base class for associative types (maps) |
52 | template <class C> |
53 | struct IndexableTraitsAssoc : public FormatTraitsBase { |
54 | typedef typename C::value_type::second_type value_type; |
55 | |
56 | static const value_type& at(const C& c, int idx) { |
57 | return c.at(static_cast<typename C::key_type>(idx)); |
58 | } |
59 | |
60 | static const value_type& at(const C& c, int idx, const value_type& dflt) { |
61 | auto pos = c.find(static_cast<typename C::key_type>(idx)); |
62 | return pos != c.end() ? pos->second : dflt; |
63 | } |
64 | }; |
65 | |
66 | } // namespace detail |
67 | } // namespace folly |
68 | |