template_util.h revision 1320f92c476a1ad9d19dba2a48c72b75566198e9
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
31// Member function pointer detection. This is built-in to C++ 11's stdlib, and
32// we can remove this when we switch to it.
33template<typename T>
34struct is_member_function_pointer : false_type {};
35
36template <typename R, typename Z, typename... A>
37struct is_member_function_pointer<R(Z::*)(A...)> : true_type {};
38template <typename R, typename Z, typename... A>
39struct is_member_function_pointer<R(Z::*)(A...) const> : true_type {};
40
41
42template <class T, class U> struct is_same : public false_type {};
43template <class T> struct is_same<T,T> : true_type {};
44
45template<class> struct is_array : public false_type {};
46template<class T, size_t n> struct is_array<T[n]> : public true_type {};
47template<class T> struct is_array<T[]> : public true_type {};
48
49template <class T> struct is_non_const_reference : false_type {};
50template <class T> struct is_non_const_reference<T&> : true_type {};
51template <class T> struct is_non_const_reference<const T&> : false_type {};
52
53template <class T> struct is_const : false_type {};
54template <class T> struct is_const<const T> : true_type {};
55
56template <class T> struct is_void : false_type {};
57template <> struct is_void<void> : true_type {};
58
59namespace internal {
60
61// Types YesType and NoType are guaranteed such that sizeof(YesType) <
62// sizeof(NoType).
63typedef char YesType;
64
65struct NoType {
66  YesType dummy[2];
67};
68
69// This class is an implementation detail for is_convertible, and you
70// don't need to know how it works to use is_convertible. For those
71// who care: we declare two different functions, one whose argument is
72// of type To and one with a variadic argument list. We give them
73// return types of different size, so we can use sizeof to trick the
74// compiler into telling us which function it would have chosen if we
75// had called it with an argument of type From.  See Alexandrescu's
76// _Modern C++ Design_ for more details on this sort of trick.
77
78struct ConvertHelper {
79  template <typename To>
80  static YesType Test(To);
81
82  template <typename To>
83  static NoType Test(...);
84
85  template <typename From>
86  static From& Create();
87};
88
89// Used to determine if a type is a struct/union/class. Inspired by Boost's
90// is_class type_trait implementation.
91struct IsClassHelper {
92  template <typename C>
93  static YesType Test(void(C::*)(void));
94
95  template <typename C>
96  static NoType Test(...);
97};
98
99}  // namespace internal
100
101// Inherits from true_type if From is convertible to To, false_type otherwise.
102//
103// Note that if the type is convertible, this will be a true_type REGARDLESS
104// of whether or not the conversion would emit a warning.
105template <typename From, typename To>
106struct is_convertible
107    : integral_constant<bool,
108                        sizeof(internal::ConvertHelper::Test<To>(
109                                   internal::ConvertHelper::Create<From>())) ==
110                        sizeof(internal::YesType)> {
111};
112
113template <typename T>
114struct is_class
115    : integral_constant<bool,
116                        sizeof(internal::IsClassHelper::Test<T>(0)) ==
117                            sizeof(internal::YesType)> {
118};
119
120template<bool B, class T = void>
121struct enable_if {};
122
123template<class T>
124struct enable_if<true, T> { typedef T type; };
125
126}  // namespace base
127
128#endif  // BASE_TEMPLATE_UTIL_H_
129