The Tor Browser: security/sandbox/chromium/base/template

     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.

     5 #ifndef BASE_TEMPLATE_UTIL_H_

     6 #define BASE_TEMPLATE_UTIL_H_

     8 #include <cstddef>  // For size_t.

    10 #include "build/build_config.h"

    12 namespace base {

    14 // template definitions from tr1

    16 template<class T, T v>

    17 struct integral_constant {

    18   static const T value = v;

    19   typedef T value_type;

    20   typedef integral_constant<T, v> type;

    21 };

    23 template <class T, T v> const T integral_constant<T, v>::value;

    25 typedef integral_constant<bool, true> true_type;

    26 typedef integral_constant<bool, false> false_type;

    28 template <class T> struct is_pointer : false_type {};

    29 template <class T> struct is_pointer<T*> : true_type {};

    31 template <class T, class U> struct is_same : public false_type {};

    32 template <class T> struct is_same<T,T> : true_type {};

    34 template<class> struct is_array : public false_type {};

    35 template<class T, size_t n> struct is_array<T[n]> : public true_type {};

    36 template<class T> struct is_array<T[]> : public true_type {};

    38 template <class T> struct is_non_const_reference : false_type {};

    39 template <class T> struct is_non_const_reference<T&> : true_type {};

    40 template <class T> struct is_non_const_reference<const T&> : false_type {};

    42 template <class T> struct is_void : false_type {};

    43 template <> struct is_void<void> : true_type {};

    45 namespace internal {

    47 // Types YesType and NoType are guaranteed such that sizeof(YesType) <

    48 // sizeof(NoType).

    49 typedef char YesType;

    51 struct NoType {

    52   YesType dummy[2];

    53 };

    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.

    64 struct ConvertHelper {

    65   template <typename To>

    66   static YesType Test(To);

    68   template <typename To>

    69   static NoType Test(...);

    71   template <typename From>

    72   static From& Create();

    73 };

    75 // Used to determine if a type is a struct/union/class. Inspired by Boost's

    76 // is_class type_trait implementation.

    77 struct IsClassHelper {

    78   template <typename C>

    79   static YesType Test(void(C::*)(void));

    81   template <typename C>

    82   static NoType Test(...);

    83 };

    85 }  // namespace internal

    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.

    91 template <typename From, typename To>

    92 struct is_convertible

    93     : integral_constant<bool,

    94                         sizeof(internal::ConvertHelper::Test<To>(

    95                                    internal::ConvertHelper::Create<From>())) ==

    96                         sizeof(internal::YesType)> {

    97 };

    99 template <typename T>

   100 struct is_class

   101     : integral_constant<bool,

   102                         sizeof(internal::IsClassHelper::Test<T>(0)) ==

   103                             sizeof(internal::YesType)> {

   104 };

   106 }  // namespace base

   108 #endif  // BASE_TEMPLATE_UTIL_H_

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