C++/STL/type traits

type traits是C++11引入的STL的一个头文件，用于类型支持。

帮助类

• template <class T, T v> struct integral_constant; //详见下定义
• template <bool B> using bool_constant = integral_constant<bool, B>;
• using true_type = bool_constant<true>;
• using false_type = bool_constant<false>;

namespace std {
 template <class T, T v>
 struct integral_constant {
   static constexpr T value = v;
   using value_type = T;
   using type = integral_constant<T, v>;
   constexpr operator value_type() const noexcept { return value; }
   constexpr value_type operator()() const noexcept { return value; }
 };
}

基本类型分类

 template <class T> struct is_void;
 template <class T> struct is_null_pointer;
 template <class T> struct is_integral;
 template <class T> struct is_floating_point;
 template <class T> struct is_array;
 template <class T> struct is_bounded_array;
 template <class T> struct is_unbounded_array;
 template <class T> struct is_pointer;
 template <class T> struct is_lvalue_reference;
 template <class T> struct is_rvalue_reference;
 template <class T> struct is_member_object_pointer;
 template <class T> struct is_member_function_pointer;
 template <class T> struct is_enum;
 template <class T> struct is_union;
 template <class T> struct is_class;
 template <class T> struct is_function;

复合类型分类

 template <class T> struct is_reference;
 template <class T> struct is_arithmetic;
 template <class T> struct is_fundamental;
 template <class T> struct is_object;
 template <class T> struct is_scalar;
 template <class T> struct is_compound;
 template <class T> struct is_member_pointer;

类型属性

 template <class T> struct is_const;
 template <class T> struct is_volatile;
 template <class T> struct is_trivial;
 template <class T> struct is_trivially_copyable;
 template <class T> struct is_standard_layout;
 template <class T> struct is_pod;
 template <class T> struct is_empty;
 template <class T> struct is_polymorphic;
 template <class T> struct is_abstract;
 template <class T> struct is_final;
 template <class T> struct is_aggregate;
 template <class T> struct is_signed;
 template <class T> struct is_unsigned;
 template <class T, class... Args> struct is_constructible;
 template <class T> struct is_default_constructible;
 template <class T> struct is_copy_constructible;
 template <class T> struct is_move_constructible;
 template <class T, class U> struct is_assignable;
 template <class T> struct is_copy_assignable;
 template <class T> struct is_move_assignable;
 template <class T, class U> struct is_swappable_with;
 template <class T> struct is_swappable;
 template <class T> struct is_destructible;
 template <class T, class... Args> struct is_trivially_constructible;
 template <class T> struct is_trivially_default_constructible;
 template <class T> struct is_trivially_copy_constructible;
 template <class T> struct is_trivially_move_constructible;
 template <class T, class U> struct is_trivially_assignable;
 template <class T> struct is_trivially_copy_assignable;
 template <class T> struct is_trivially_move_assignable;
 template <class T> struct is_trivially_destructible;
 template <class T, class... Args> struct is_nothrow_constructible;
 template <class T> struct is_nothrow_default_constructible;
 template <class T> struct is_nothrow_copy_constructible;
 template <class T> struct is_nothrow_move_constructible;
 template <class T, class U> struct is_nothrow_assignable;
 template <class T> struct is_nothrow_copy_assignable;
 template <class T> struct is_nothrow_move_assignable;
 template <class T, class U> struct is_nothrow_swappable_with;
 template <class T> struct is_nothrow_swappable;
 template <class T> struct is_nothrow_destructible;
 template <class T> struct has_virtual_destructor;
 template <class T> struct has_unique_object_representations;

类型属性查询

 template <class T> struct alignment_of;
 template <class T> struct rank; //获取数组的维数
 template <class T, unsigned I = 0> struct extent;

类型关系

 template <class T, class U> struct is_same;
 template <class Base, class Derived> struct is_base_of;
 template <class From, class To> struct is_convertible;
 template <class Fn, class... ArgTypes> struct is_invocable;
 template <class R, class Fn, class... ArgTypes> struct is_invocable_r;
 template <class Fn, class... ArgTypes> struct is_nothrow_invocable;
 template <class R, class Fn, class... ArgTypes> struct is_nothrow_invocable_r;

const-volatile修改

 template <class T> struct remove_const;
 template <class T> struct remove_volatile;
 template <class T> struct remove_cv;
 template <class T> struct add_const;
 template <class T> struct add_volatile;
 template <class T> struct add_cv;
 template <class T>
 using remove_const_t = typename remove_const<T>::type;
 template <class T>
 using remove_volatile_t = typename remove_volatile<T>::type;
 template <class T>
 using remove_cv_t = typename remove_cv<T>::type;
 template <class T>
 using add_const_t = typename add_const<T>::type;
 template <class T>
 using add_volatile_t = typename add_volatile<T>::type;
 template <class T>
 using add_cv_t = typename add_cv<T>::type;

引用修改

 template <class T> struct remove_reference;
 template <class T> struct add_lvalue_reference;
 template <class T> struct add_rvalue_reference;
 template <class T>
 using remove_reference_t = typename remove_reference<T>::type;
 template <class T>
 using add_lvalue_reference_t = typename add_lvalue_reference<T>::type;
 template <class T>
 using add_rvalue_reference_t = typename add_rvalue_reference<T>::type;

符号修改

 template <class T> struct make_signed;
 template <class T> struct make_unsigned;
 template <class T>
 using make_signed_t = typename make_signed<T>::type;
 template <class T>
 using make_unsigned_t = typename make_unsigned<T>::type;

数组修改

• template <class T> struct remove_extent; 去除数组类型的最外一个维度，如果不是数组则返回该类型本身。

 template <class T> struct remove_all_extents;
 template <class T>
 using remove_extent_t = typename remove_extent<T>::type;
 template <class T>
 using remove_all_extents_t = typename remove_all_extents<T>::type;

指针修改

 template <class T> struct remove_pointer;
 template <class T> struct add_pointer;
 template <class T>
 using remove_pointer_t = typename remove_pointer<T>::type;
 template <class T>
 using add_pointer_t = typename add_pointer<T>::type;

其它变换

• template <size_t Len, size_t Align = /*default-alignment*/ > struct aligned_storage; 给出需要的长度和对齐要求，返回一个类型。通常用于定义一个未初始化的内存空间，使用占位new运算符初始化，显式使用析构函数来销毁对象。
• template <size_t Len, size_t Align = /*default-alignment*/ > using aligned_storage_t = typename aligned_storage<Len, Align>::type;帮助类
• template <size_t Len, class... Types> struct aligned_union; 返回一个类型，可以满足内存对齐的要求下，足以容纳各种类型及至少Len字节长度。
• template <class T> struct decay; 实现了lvalue-to-rvalue, array-to-pointer, function-to-pointer的类型隐式转换。

 template <class T> struct remove_cvref;
 template <bool, class T = void> struct enable_if;
 template <bool, class T, class F> struct conditional;
 template <class... T> struct common_type;
 template <class T> struct underlying_type;
 template <class> class result_of; // not defined
 template <class F, class... ArgTypes> class result_of<F(ArgTypes...)>;
 template <class F, class... ArgTypes> class invoke_result;
 template <size_t Len, class... Types>  using aligned_union_t = typename aligned_union<Len, Types...>::type;
 template <class T>  using decay_t = typename decay<T>::type;
 template <class T>  using remove_cvref_t = typename remove_cvref<T>::type;
 template <bool b, class T = void>  using enable_if_t = typename enable_if<b, T>::type;
 template <bool b, class T, class F>  using conditional_t = typename conditional<b, T, F>::type;
 template <class... T>  using common_type_t = typename common_type<T...>::type;
 template <class T>  using underlying_type_t = typename underlying_type<T>::type;
 template <class T>  using result_of_t = typename result_of<T>::type;
 template <class F, class... ArgTypes>   using invoke_result_t = typename invoke_result<F, ArgTypes...>::type;
 template <class...>  using void_t = void;

逻辑操作符特性类

 template<class... B> struct conjunction;
 template<class... B> struct disjunction;
 template<class B> struct negation;

endian

 enum class endian {
   little = /*implementation-defined*/,
   big    = /*implementation-defined*/,
   native = /*implementation-defined*/
 };

主类型分类

 template <class T> inline constexpr bool is_void_v  = is_void<T>::value;
 template <class T> inline constexpr bool is_null_pointer_v  = is_null_pointer<T>::value;
 template <class T> inline constexpr bool is_integral_v  = is_integral<T>::value;
 template <class T> inline constexpr bool is_floating_point_v  = is_floating_point<T>::value;
 template <class T> inline constexpr bool is_array_v  = is_array<T>::value;
 template< class T > constexpr bool is_bounded_array_v = is_bounded_array<T>::value;
 template< class T > constexpr bool is_unbounded_array_v = is_bounded_array<T>::value;
 template <class T> inline constexpr bool is_pointer_v  = is_pointer<T>::value;
 template <class T> inline constexpr bool is_lvalue_reference_v  = is_lvalue_reference<T>::value;
 template <class T> inline constexpr bool is_rvalue_reference_v  = is_rvalue_reference<T>::value;
 template <class T> inline constexpr bool is_member_object_pointer_v  = is_member_object_pointer<T>::value;
 template <class T> inline constexpr bool is_member_function_pointer_v  = is_member_function_pointer<T>::value;
 template <class T> inline constexpr bool is_enum_v  = is_enum<T>::value;
 template <class T> inline constexpr bool is_union_v  = is_union<T>::value;
 template <class T> inline constexpr bool is_class_v  = is_class<T>::value;
 template <class T> inline constexpr bool is_function_v  = is_function<T>::value;

复合类型分类

 template <class T> inline constexpr bool is_reference_v  = is_reference<T>::value;
 template <class T> inline constexpr bool is_arithmetic_v  = is_arithmetic<T>::value;
 template <class T> inline constexpr bool is_fundamental_v  = is_fundamental<T>::value;
 template <class T> inline constexpr bool is_object_v  = is_object<T>::value;
 template <class T> inline constexpr bool is_scalar_v  = is_scalar<T>::value;
 template <class T> inline constexpr bool is_compound_v  = is_compound<T>::value;
 template <class T> inline constexpr bool is_member_pointer_v  = is_member_pointer<T>::value;

类型属性

 template <class T> inline constexpr bool is_const_v  = is_const<T>::value;
 template <class T> inline constexpr bool is_volatile_v  = is_volatile<T>::value;
 template <class T> inline constexpr bool is_trivial_v  = is_trivial<T>::value;
 template <class T> inline constexpr bool is_trivially_copyable_v  = is_trivially_copyable<T>::value;
 template <class T> inline constexpr bool is_standard_layout_v  = is_standard_layout<T>::value;
 template <class T> inline constexpr bool is_pod_v  = is_pod<T>::value;
 template <class T> inline constexpr bool is_empty_v  = is_empty<T>::value;
 template <class T> inline constexpr bool is_polymorphic_v  = is_polymorphic<T>::value;
 template <class T> inline constexpr bool is_abstract_v  = is_abstract<T>::value;
 template <class T> inline constexpr bool is_final_v  = is_final<T>::value;
 template <class T> inline constexpr bool is_aggregate_v  = is_aggregate<T>::value;
 template <class T> inline constexpr bool is_signed_v  = is_signed<T>::value;
 template <class T> inline constexpr bool is_unsigned_v  = is_unsigned<T>::value;
 template <class T, class... Args> inline constexpr bool is_constructible_v  = is_constructible<T, Args...>::value;
 template <class T> inline constexpr bool is_default_constructible_v  = is_default_constructible<T>::value;
 template <class T> inline constexpr bool is_copy_constructible_v  = is_copy_constructible<T>::value;
 template <class T> inline constexpr bool is_move_constructible_v  = is_move_constructible<T>::value;
 template <class T, class U> inline constexpr bool is_assignable_v  = is_assignable<T, U>::value;
 template <class T> inline constexpr bool is_copy_assignable_v  = is_copy_assignable<T>::value;
 template <class T> inline constexpr bool is_move_assignable_v  = is_move_assignable<T>::value;
 template <class T, class U> inline constexpr bool is_swappable_with_v  = is_swappable_with<T, U>::value;
 template <class T> inline constexpr bool is_swappable_v  = is_swappable<T>::value;
 template <class T> inline constexpr bool is_destructible_v  = is_destructible<T>::value;
 template <class T, class... Args> inline constexpr bool is_trivially_constructible_v  = is_trivially_constructible<T, Args...>::value;
 template <class T> inline constexpr bool is_trivially_default_constructible_v  = is_trivially_default_constructible<T>::value;
 template <class T> inline constexpr bool is_trivially_copy_constructible_v  = is_trivially_copy_constructible<T>::value;
 template <class T> inline constexpr bool is_trivially_move_constructible_v  = is_trivially_move_constructible<T>::value;
 template <class T, class U> inline constexpr bool is_trivially_assignable_v  = is_trivially_assignable<T, U>::value;
 template <class T> inline constexpr bool is_trivially_copy_assignable_v  = is_trivially_copy_assignable<T>::value;
 template <class T> inline constexpr bool is_trivially_move_assignable_v  = is_trivially_move_assignable<T>::value;
 template <class T> inline constexpr bool is_trivially_destructible_v  = is_trivially_destructible<T>::value;
 template <class T, class... Args> inline constexpr bool is_nothrow_constructible_v  = is_nothrow_constructible<T, Args...>::value;
 template <class T> inline constexpr bool is_nothrow_default_constructible_v  = is_nothrow_default_constructible<T>::value;
 template <class T> inline constexpr bool is_nothrow_copy_constructible_v  = is_nothrow_copy_constructible<T>::value;
 template <class T> inline constexpr bool is_nothrow_move_constructible_v  = is_nothrow_move_constructible<T>::value;
 template <class T, class U> inline constexpr bool is_nothrow_assignable_v  = is_nothrow_assignable<T, U>::value;
 template <class T> inline constexpr bool is_nothrow_copy_assignable_v  = is_nothrow_copy_assignable<T>::value;
 template <class T> inline constexpr bool is_nothrow_move_assignable_v  = is_nothrow_move_assignable<T>::value;
 template <class T, class U> inline constexpr bool is_nothrow_swappable_with_v  = is_nothrow_swappable_with<T, U>::value;
 template <class T> inline constexpr bool is_nothrow_swappable_v  = is_nothrow_swappable<T>::value;
 template <class T> inline constexpr bool is_nothrow_destructible_v  = is_nothrow_destructible<T>::value;
 template <class T> inline constexpr bool has_virtual_destructor_v  = has_virtual_destructor<T>::value;
 template <class T> inline constexpr bool has_unique_object_representations_v  = has_unique_object_representations<T>::value;

类型属性查询

 template <class T> inline constexpr size_t alignment_of_v  = alignment_of<T>::value;
 template <class T> inline constexpr size_t rank_v  = rank<T>::value;
 template <class T, unsigned I = 0> inline constexpr size_t extent_v  = extent<T, I>::value;

类型关系

 template <class T, class U> inline constexpr bool is_same_v  = is_same<T, U>::value;
 template <class Base, class Derived> inline constexpr bool is_base_of_v  = is_base_of<Base, Derived>::value;
 template <class From, class To> inline constexpr bool is_convertible_v  = is_convertible<From, To>::value;

 template <class Fn, class... ArgTypes>   inline constexpr bool is_invocable_v    = is_invocable<Fn, ArgTypes...>::value;
 template <class R, class Fn, class... ArgTypes>  inline constexpr bool is_invocable_r_v    = is_invocable_r<R, Fn, ArgTypes...>::value;
 template <class Fn, class... ArgTypes>  inline constexpr bool is_nothrow_invocable_v    = is_nothrow_invocable<Fn, ArgTypes...>::value;
 template <class R, class Fn, class... ArgTypes>  inline constexpr bool is_nothrow_invocable_r_v    = is_nothrow_invocable_r<R, Fn, ArgTypes...>::value;

逻辑操作符特性类

 template<class... B> inline constexpr bool conjunction_v = conjunction<B...>::value;
 template<class... B> inline constexpr bool disjunction_v = disjunction<B...>::value;
 template<class B> inline constexpr bool negation_v = negation::value;