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 
atIndexableTraitsSeq42   static const value_type& at(const C& c, int idx) { return c.at(idx); }
43 
atIndexableTraitsSeq44   static const value_type& at(const C& c, int idx, const value_type& dflt) {
45     return (idx >= 0 && size_t(idx) < c.size()) ? c.at(idx) : dflt;
46   }
47 };
48 
49 // Base class for associative types (maps)
50 template <class C>
51 struct IndexableTraitsAssoc : public FormatTraitsBase {
52   typedef typename C::value_type::second_type value_type;
53 
atIndexableTraitsAssoc54   static const value_type& at(const C& c, int idx) {
55     return c.at(static_cast<typename C::key_type>(idx));
56   }
57 
atIndexableTraitsAssoc58   static const value_type& at(const C& c, int idx, const value_type& dflt) {
59     auto pos = c.find(static_cast<typename C::key_type>(idx));
60     return pos != c.end() ? pos->second : dflt;
61   }
62 };
63 
64 } // namespace detail
65 } // namespace folly
66