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1 // Copyright (c) 2010 The Chromium Authors. All rights reserved. | 1 // Copyright (c) 2010 The Chromium Authors. All rights reserved. |
2 // Use of this source code is governed by a BSD-style license that can be | 2 // Use of this source code is governed by a BSD-style license that can be |
3 // found in the LICENSE file. | 3 // found in the LICENSE file. |
4 | 4 |
5 #ifndef BASE_TEMPLATE_UTIL_H_ | 5 #ifndef BASE_TEMPLATE_UTIL_H_ |
6 #define BASE_TEMPLATE_UTIL_H_ | 6 #define BASE_TEMPLATE_UTIL_H_ |
7 #pragma once | 7 #pragma once |
8 | 8 |
9 #include "build/build_config.h" | |
10 | |
11 namespace base { | 9 namespace base { |
12 | 10 |
13 // template definitions from tr1 | 11 // template definitions from tr1 |
14 | 12 |
15 template<class T, T v> | 13 template<class T, T v> |
16 struct integral_constant { | 14 struct integral_constant { |
17 static const T value = v; | 15 static const T value = v; |
18 typedef T value_type; | 16 typedef T value_type; |
19 typedef integral_constant<T, v> type; | 17 typedef integral_constant<T, v> type; |
20 }; | 18 }; |
21 | 19 |
22 template <class T, T v> const T integral_constant<T, v>::value; | 20 template <class T, T v> const T integral_constant<T, v>::value; |
23 | 21 |
24 typedef integral_constant<bool, true> true_type; | 22 typedef integral_constant<bool, true> true_type; |
25 typedef integral_constant<bool, false> false_type; | 23 typedef integral_constant<bool, false> false_type; |
26 | 24 |
27 template <class T> struct is_pointer : false_type {}; | 25 template <class T> struct is_pointer : false_type {}; |
28 template <class T> struct is_pointer<T*> : true_type {}; | 26 template <class T> struct is_pointer<T*> : true_type {}; |
29 | 27 |
30 namespace internal { | |
31 | |
32 // Types small_ and big_ are guaranteed such that sizeof(small_) < | |
33 // sizeof(big_) | |
34 typedef char small_; | |
35 | |
36 struct big_ { | |
37 small_ dummy[2]; | |
38 }; | |
39 | |
40 #if !defined(OS_WIN) | |
41 | |
42 // This class is an implementation detail for is_convertible, and you | |
43 // don't need to know how it works to use is_convertible. For those | |
44 // who care: we declare two different functions, one whose argument is | |
45 // of type To and one with a variadic argument list. We give them | |
46 // return types of different size, so we can use sizeof to trick the | |
47 // compiler into telling us which function it would have chosen if we | |
48 // had called it with an argument of type From. See Alexandrescu's | |
49 // _Modern C++ Design_ for more details on this sort of trick. | |
50 | |
51 template <typename From, typename To> | |
52 struct ConvertHelper { | |
53 static small_ Test(To); | |
54 static big_ Test(...); | |
55 static From Create(); | |
56 }; | |
57 | |
58 #endif // !defined(OS_WIN) | |
59 | |
60 } // namespace internal | |
61 | |
62 #if !defined(OS_WIN) | |
63 | |
64 // Inherits from true_type if From is convertible to To, false_type otherwise. | |
65 template <typename From, typename To> | |
66 struct is_convertible | |
67 : integral_constant<bool, | |
68 sizeof(internal::ConvertHelper<From, To>::Test( | |
69 internal::ConvertHelper<From, To>::Create())) | |
70 == sizeof(internal::small_)> { | |
71 }; | |
72 | |
73 #endif // !defined(OS_WIN) | |
74 | |
75 } // namespace base | 28 } // namespace base |
76 | 29 |
77 #endif // BASE_TEMPLATE_UTIL_H_ | 30 #endif // BASE_TEMPLATE_UTIL_H_ |
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