C++ Utilities  4.17.0
Useful C++ classes and routines such as argument parser, IO and conversion utilities
traits.h
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1 #ifndef CPP_UTILITIES_TRAITS_H
2 #define CPP_UTILITIES_TRAITS_H
3 
4 #include <iterator>
5 #include <type_traits>
6 
8 namespace Traits {
9 
11 namespace Detail {
12 enum class Enabler {};
13 }
15 
17 template <typename If, typename Then, typename Else> using Conditional = typename std::conditional<If::value, Then, Else>::type;
18 
20 template <bool B, typename...> struct Bool : std::integral_constant<bool, B> {
21 };
22 
24 template <typename T> using Not = Bool<!T::value>;
25 
27 template <typename... T> struct Any : Bool<false> {
28 };
30 template <typename Head, typename... Tail> struct Any<Head, Tail...> : Conditional<Head, Bool<true>, Any<Tail...>> {
31 };
32 
34 template <typename... T> struct All : Bool<true> {
35 };
37 template <typename Head, typename... Tail> struct All<Head, Tail...> : Conditional<Head, All<Tail...>, Bool<false>> {
38 };
39 
41 template <typename... T> struct None : Bool<true> {
42 };
44 template <typename Head, typename... Tail> struct None<Head, Tail...> : Conditional<Head, Bool<false>, None<Tail...>> {
45 };
46 
48 template <typename... Condition> using EnableIf = typename std::enable_if<All<Condition...>::value, Detail::Enabler>::type;
50 template <typename... Condition> using DisableIf = typename std::enable_if<!All<Condition...>::value, Detail::Enabler>::type;
51 
53 template <typename... Condition> using EnableIfAny = typename std::enable_if<Any<Condition...>::value, Detail::Enabler>::type;
55 template <typename... Condition> using DisableIfAny = typename std::enable_if<!Any<Condition...>::value, Detail::Enabler>::type;
56 
58 namespace Detail {
59 template <typename T, template <typename...> class Template> struct IsSpecializationOfHelper : Bool<false> {
60 };
61 template <template <typename...> class Template, typename... Args> struct IsSpecializationOfHelper<Template<Args...>, Template> : Bool<true> {
62 };
63 } // namespace Detail
66 template <typename Type, template <typename...> class... TemplateTypes>
67 struct IsSpecializationOf : Detail::IsSpecializationOfHelper<typename std::remove_cv<Type>::type, TemplateTypes...> {
68 };
70 template <typename Type, template <typename...> class... TemplateTypes> struct IsSpecializingAnyOf : Bool<false> {
71 };
73 template <typename Type, template <typename...> class TemplateType, template <typename...> class... RemainingTemplateTypes>
74 struct IsSpecializingAnyOf<Type, TemplateType, RemainingTemplateTypes...>
75  : Conditional<IsSpecializationOf<Type, TemplateType>, Bool<true>, IsSpecializingAnyOf<Type, RemainingTemplateTypes...>> {
76 };
77 
79 template <typename... T> struct IsAnyOf : Bool<false> {
80 };
82 template <typename Type, typename OtherType, typename... RemainingTypes>
83 struct IsAnyOf<Type, OtherType, RemainingTypes...> : Conditional<std::is_same<Type, OtherType>, Bool<true>, IsAnyOf<Type, RemainingTypes...>> {
84 };
86 template <typename... T> struct IsNoneOf : Bool<true> {
87 };
89 template <typename Type, typename OtherType, typename... RemainingTypes>
90 struct IsNoneOf<Type, OtherType, RemainingTypes...> : Conditional<std::is_same<Type, OtherType>, Bool<false>, IsNoneOf<Type, RemainingTypes...>> {
91 };
92 
94 template <typename T>
95 struct IsCString
96  : Bool<std::is_same<char const *, typename std::decay<T>::type>::value || std::is_same<char *, typename std::decay<T>::type>::value> {
97 };
99 template <typename T> struct IsString : Bool<IsCString<T>::value || IsSpecializationOf<T, std::basic_string>::value> {
100 };
101 
103 template <typename T, typename = void> struct IsComplete : Bool<false> {
104 };
106 template <typename T> struct IsComplete<T, decltype(void(sizeof(T)))> : Bool<true> {
107 };
108 
113 #define CPP_UTILITIES_PP_COMMA ,
114 
121 #define CPP_UTILITIES_TRAITS_DEFINE_TYPE_CHECK(CheckName, CheckCode) \
122  namespace Detail { \
123  template <typename T> auto CheckName(int) -> decltype(CheckCode, ::Traits::Bool<true>{}); \
124  template <typename T>::Traits::Bool<false> CheckName(...); \
125  } \
126  template <typename T> using CheckName = decltype(Detail::CheckName<T>(0))
127 
129 CPP_UTILITIES_TRAITS_DEFINE_TYPE_CHECK(IsDereferencable, *(std::declval<T &>()));
130 
132 CPP_UTILITIES_TRAITS_DEFINE_TYPE_CHECK(HasSize, std::is_integral<decltype(std::declval<T &>().size())>::value);
133 
135 CPP_UTILITIES_TRAITS_DEFINE_TYPE_CHECK(IsReservable, std::declval<T &>().reserve(0u));
136 
138 CPP_UTILITIES_TRAITS_DEFINE_TYPE_CHECK(IsResizable, std::declval<T &>().resize(0u));
139 
141 CPP_UTILITIES_TRAITS_DEFINE_TYPE_CHECK(HasOperatorBool, std::declval<T &>() ? true : false);
142 
145  // begin/end and operator !=
146  std::begin(std::declval<T &>())
147  != std::end(std::declval<T &>()) CPP_UTILITIES_PP_COMMA
148  // operator ,
150  // operator ++
151  ++ std::declval<decltype(begin(std::declval<T &>())) &>() CPP_UTILITIES_PP_COMMA
152  // operator*
153  void(*begin(std::declval<T &>())));
154 
156 template <typename T, EnableIf<IsDereferencable<T>> * = nullptr> constexpr auto &dereferenceMaybe(T &value)
157 {
158  return *value;
159 }
160 
162 template <typename T, DisableIf<IsDereferencable<T>> * = nullptr> constexpr auto &dereferenceMaybe(T &value)
163 {
164  return value;
165 }
166 
168 template <typename T, EnableIf<IsDereferencable<T>> * = nullptr> constexpr const auto &dereferenceMaybe(const T &value)
169 {
170  return *value;
171 }
172 
174 template <typename T, DisableIf<IsDereferencable<T>> * = nullptr> constexpr const auto &dereferenceMaybe(const T &value)
175 {
176  return value;
177 }
178 
179 } // namespace Traits
180 
181 #endif // CPP_UTILITIES_TRAITS_H
constexpr auto & dereferenceMaybe(T &value)
Dereferences the specified value if possible; otherwise just returns value itself.
Definition: traits.h:156
Evaluates to Bool<true> if the specified type is any of the specified types; otherwise evaluates to B...
Definition: traits.h:79
Evaluates to Bool<true> if the specified type is based on the specified.
Definition: traits.h:67
Evaluates to Bool<true> if the specified type is complete; if the type is only forward-declared it ev...
Definition: traits.h:103
Evaluates to Bool<true> if all specified conditions are true; otherwise evaluates to Bool<false>.
Definition: traits.h:34
Evaluates to Bool<true> if the specified type is based on one of the specified templates; otherwise e...
Definition: traits.h:70
typename std::enable_if< All< Condition... >::value, Detail::Enabler >::type EnableIf
Shortcut for std::enable_if to omit ::value and ::type.
Definition: traits.h:48
Evaluates to Bool<true> if the specified type is a C-string (char * or const char *); otherwise evalu...
Definition: traits.h:95
#define CPP_UTILITIES_PP_COMMA
The CPP_UTILITIES_PP_COMMA macro helps passing "," as a macro argument.
Definition: traits.h:113
typename std::conditional< If::value, Then, Else >::type Conditional
Shortcut for std::conditional to omit ::value and ::type.
Definition: traits.h:17
Evaluates to Bool<true> if the specified type is none of the specified types; otherwise evaluates to ...
Definition: traits.h:86
typename std::enable_if<!Any< Condition... >::value, Detail::Enabler >::type DisableIfAny
Shortcut for std::enable_if to apply Traits::Any, negate the condition and omit ::value and ::type.
Definition: traits.h:55
typename std::enable_if<!All< Condition... >::value, Detail::Enabler >::type DisableIf
Shortcut for std::enable_if to negate the condition and omit ::value and ::type.
Definition: traits.h:50
Evaluates to Bool<true> if at least one of the specified conditions is true; otherwise evaluates to B...
Definition: traits.h:27
Evaluates to Bool<true> if the specified type is a C-string (char * or const char *); otherwise evalu...
Definition: traits.h:99
typename std::enable_if< Any< Condition... >::value, Detail::Enabler >::type EnableIfAny
Shortcut for std::enable_if to apply Traits::Any and omit ::value and ::type.
Definition: traits.h:53
Evaluates to Bool<true> if none of the specified conditions are true; otherwise evaluates to Bool<fal...
Definition: traits.h:41
CPP_UTILITIES_TRAITS_DEFINE_TYPE_CHECK(IsDereferencable, *(std::declval< T & >()))
Evaluates to Bool<true> if the specified type can be dereferenced using the *-operator; otherwise eva...
Contains traits for conveniently exploiting SFINAE.
Definition: traits.h:8
Wraps a static boolean constant.
Definition: traits.h:20