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