template_util.h revision 5821806d5e7f356e8fa4b058a389a808ea183019
1// Copyright (c) 2011 The Chromium Authors. All rights reserved.
2// Use of this source code is governed by a BSD-style license that can be
3// found in the LICENSE file.
4
5#ifndef BASE_TEMPLATE_UTIL_H_
6#define BASE_TEMPLATE_UTIL_H_
7
8#include <cstddef>  // For size_t.
9
10#include "build/build_config.h"
11
12namespace base {
13
14// template definitions from tr1
15
16template<class T, T v>
17struct integral_constant {
18  static const T value = v;
19  typedef T value_type;
20  typedef integral_constant<T, v> type;
21};
22
23template <class T, T v> const T integral_constant<T, v>::value;
24
25typedef integral_constant<bool, true> true_type;
26typedef integral_constant<bool, false> false_type;
27
28template <class T> struct is_pointer : false_type {};
29template <class T> struct is_pointer<T*> : true_type {};
30
31template <class T, class U> struct is_same : public false_type {};
32template <class T> struct is_same<T,T> : true_type {};
33
34template<class> struct is_array : public false_type {};
35template<class T, size_t n> struct is_array<T[n]> : public true_type {};
36template<class T> struct is_array<T[]> : public true_type {};
37
38template <class T> struct is_non_const_reference : false_type {};
39template <class T> struct is_non_const_reference<T&> : true_type {};
40template <class T> struct is_non_const_reference<const T&> : false_type {};
41
42template <class T> struct is_void : false_type {};
43template <> struct is_void<void> : true_type {};
44
45namespace internal {
46
47// Types YesType and NoType are guaranteed such that sizeof(YesType) <
48// sizeof(NoType).
49typedef char YesType;
50
51struct NoType {
52  YesType dummy[2];
53};
54
55// This class is an implementation detail for is_convertible, and you
56// don't need to know how it works to use is_convertible. For those
57// who care: we declare two different functions, one whose argument is
58// of type To and one with a variadic argument list. We give them
59// return types of different size, so we can use sizeof to trick the
60// compiler into telling us which function it would have chosen if we
61// had called it with an argument of type From.  See Alexandrescu's
62// _Modern C++ Design_ for more details on this sort of trick.
63
64struct ConvertHelper {
65  template <typename To>
66  static YesType Test(To);
67
68  template <typename To>
69  static NoType Test(...);
70
71  template <typename From>
72  static From& Create();
73};
74
75// Used to determine if a type is a struct/union/class. Inspired by Boost's
76// is_class type_trait implementation.
77struct IsClassHelper {
78  template <typename C>
79  static YesType Test(void(C::*)(void));
80
81  template <typename C>
82  static NoType Test(...);
83};
84
85}  // namespace internal
86
87// Inherits from true_type if From is convertible to To, false_type otherwise.
88//
89// Note that if the type is convertible, this will be a true_type REGARDLESS
90// of whether or not the conversion would emit a warning.
91template <typename From, typename To>
92struct is_convertible
93    : integral_constant<bool,
94                        sizeof(internal::ConvertHelper::Test<To>(
95                                   internal::ConvertHelper::Create<From>())) ==
96                        sizeof(internal::YesType)> {
97};
98
99template <typename T>
100struct is_class
101    : integral_constant<bool,
102                        sizeof(internal::IsClassHelper::Test<T>(0)) ==
103                            sizeof(internal::YesType)> {
104};
105
106}  // namespace base
107
108#endif  // BASE_TEMPLATE_UTIL_H_
109