1 | // Copyright 2005 Google Inc. |
2 | // All rights reserved. |
3 | // |
4 | // Redistribution and use in source and binary forms, with or without |
5 | // modification, are permitted provided that the following conditions are |
6 | // met: |
7 | // |
8 | // * Redistributions of source code must retain the above copyright |
9 | // notice, this list of conditions and the following disclaimer. |
10 | // * Redistributions in binary form must reproduce the above |
11 | // copyright notice, this list of conditions and the following disclaimer |
12 | // in the documentation and/or other materials provided with the |
13 | // distribution. |
14 | // * Neither the name of Google Inc. nor the names of its |
15 | // contributors may be used to endorse or promote products derived from |
16 | // this software without specific prior written permission. |
17 | // |
18 | // THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS |
19 | // "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT |
20 | // LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR |
21 | // A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT |
22 | // OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, |
23 | // SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT |
24 | // LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, |
25 | // DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY |
26 | // THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT |
27 | // (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE |
28 | // OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE. |
29 | |
30 | // ---- |
31 | // |
32 | // Template metaprogramming utility functions. |
33 | // |
34 | // This code is compiled directly on many platforms, including client |
35 | // platforms like Windows, Mac, and embedded systems. Before making |
36 | // any changes here, make sure that you're not breaking any platforms. |
37 | // |
38 | // |
39 | // The names choosen here reflect those used in tr1 and the boost::mpl |
40 | // library, there are similar operations used in the Loki library as |
41 | // well. I prefer the boost names for 2 reasons: |
42 | // 1. I think that portions of the Boost libraries are more likely to |
43 | // be included in the c++ standard. |
44 | // 2. It is not impossible that some of the boost libraries will be |
45 | // included in our own build in the future. |
46 | // Both of these outcomes means that we may be able to directly replace |
47 | // some of these with boost equivalents. |
48 | // |
49 | #ifndef BASE_TEMPLATE_UTIL_H_ |
50 | #define BASE_TEMPLATE_UTIL_H_ |
51 | |
52 | #include <sparsehash/internal/sparseconfig.h> |
53 | _START_GOOGLE_NAMESPACE_ |
54 | |
55 | // Types small_ and big_ are guaranteed such that sizeof(small_) < |
56 | // sizeof(big_) |
57 | typedef char small_; |
58 | |
59 | struct big_ { |
60 | char dummy[2]; |
61 | }; |
62 | |
63 | // Identity metafunction. |
64 | template <class T> |
65 | struct identity_ { |
66 | typedef T type; |
67 | }; |
68 | |
69 | // integral_constant, defined in tr1, is a wrapper for an integer |
70 | // value. We don't really need this generality; we could get away |
71 | // with hardcoding the integer type to bool. We use the fully |
72 | // general integer_constant for compatibility with tr1. |
73 | |
74 | template<class T, T v> |
75 | struct integral_constant { |
76 | static const T value = v; |
77 | typedef T value_type; |
78 | typedef integral_constant<T, v> type; |
79 | }; |
80 | |
81 | template <class T, T v> const T integral_constant<T, v>::value; |
82 | |
83 | |
84 | // Abbreviations: true_type and false_type are structs that represent boolean |
85 | // true and false values. Also define the boost::mpl versions of those names, |
86 | // true_ and false_. |
87 | typedef integral_constant<bool, true> true_type; |
88 | typedef integral_constant<bool, false> false_type; |
89 | typedef true_type true_; |
90 | typedef false_type false_; |
91 | |
92 | // if_ is a templatized conditional statement. |
93 | // if_<cond, A, B> is a compile time evaluation of cond. |
94 | // if_<>::type contains A if cond is true, B otherwise. |
95 | template<bool cond, typename A, typename B> |
96 | struct if_{ |
97 | typedef A type; |
98 | }; |
99 | |
100 | template<typename A, typename B> |
101 | struct if_<false, A, B> { |
102 | typedef B type; |
103 | }; |
104 | |
105 | |
106 | // type_equals_ is a template type comparator, similar to Loki IsSameType. |
107 | // type_equals_<A, B>::value is true iff "A" is the same type as "B". |
108 | // |
109 | // New code should prefer base::is_same, defined in base/type_traits.h. |
110 | // It is functionally identical, but is_same is the standard spelling. |
111 | template<typename A, typename B> |
112 | struct type_equals_ : public false_ { |
113 | }; |
114 | |
115 | template<typename A> |
116 | struct type_equals_<A, A> : public true_ { |
117 | }; |
118 | |
119 | // and_ is a template && operator. |
120 | // and_<A, B>::value evaluates "A::value && B::value". |
121 | template<typename A, typename B> |
122 | struct and_ : public integral_constant<bool, (A::value && B::value)> { |
123 | }; |
124 | |
125 | // or_ is a template || operator. |
126 | // or_<A, B>::value evaluates "A::value || B::value". |
127 | template<typename A, typename B> |
128 | struct or_ : public integral_constant<bool, (A::value || B::value)> { |
129 | }; |
130 | |
131 | |
132 | _END_GOOGLE_NAMESPACE_ |
133 | |
134 | #endif // BASE_TEMPLATE_UTIL_H_ |
135 | |