std::is_scoped_enum

 

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类型类别 is_void (C++11) is_null_pointer (C++11)(DR*) is_array (C++11) is_pointer (C++11) is_enum (C++11) is_union (C++11) is_class (C++11) is_function (C++11) is_reference (C++11)  is_object (C++11) is_scalar (C++11) is_compound (C++11) is_integral (C++11) is_floating_point (C++11)   is_fundamental (C++11) is_arithmetic (C++11) is_lvalue_reference (C++11) is_rvalue_reference (C++11) is_member_pointer (C++11) is_member_object_pointer (C++11) is_member_function_pointer (C++11) 类型属性 is_const (C++11) is_volatile (C++11) is_empty (C++11) is_polymorphic (C++11) is_final (C++14) is_abstract (C++11) is_aggregate (C++17) is_implicit_lifetime (C++23) is_trivial (C++11)(deprecated in C++26) is_trivially_copyable (C++11) is_standard_layout (C++11) is_literal_type (C++11)(until C++20*) is_pod (C++11)(deprecated in C++20) is_signed (C++11) is_unsigned (C++11) is_bounded_array (C++20) is_unbounded_array (C++20) is_scoped_enum (C++23) has_unique_object_representations (C++17) 类型特性常量 integral_constantbool_constanttrue_typefalse_type (C++11)(C++17)(C++11)(C++11) 元函数 conjunction (C++17) disjunction (C++17) negation (C++17)	支持的操作 is_constructibleis_trivially_constructibleis_nothrow_constructible (C++11)(C++11)(C++11) is_default_constructibleis_trivially_default_constructibleis_nothrow_default_constructible (C++11)(C++11)(C++11) is_copy_constructibleis_trivially_copy_constructibleis_nothrow_copy_constructible (C++11)(C++11)(C++11) is_move_constructibleis_trivially_move_constructibleis_nothrow_move_constructible (C++11)(C++11)(C++11) is_assignableis_trivially_assignableis_nothrow_assignable (C++11)(C++11)(C++11) is_copy_assignableis_trivially_copy_assignableis_nothrow_copy_assignable (C++11)(C++11)(C++11) is_move_assignableis_trivially_move_assignableis_nothrow_move_assignable (C++11)(C++11)(C++11) is_destructibleis_trivially_destructibleis_nothrow_destructible (C++11)(C++11)(C++11) has_virtual_destructor (C++11) is_swappable_withis_swappableis_nothrow_swappable_withis_nothrow_swappable (C++17)(C++17)(C++17)(C++17) 关系和属性查询 is_same (C++11) is_convertibleis_nothrow_convertible (C++11)(C++20) is_layout_compatible (C++20) is_pointer_interconvertible_base_of (C++20) is_pointer_interconvertible_with_class (C++20)   is_corresponding_member (C++20) reference_constructs_from_temporary (C++23) reference_converts_from_temporary (C++23) is_base_of (C++11) is_virtual_base_of (C++26) alignment_of (C++11) rank (C++11) extent (C++11) is_invocableis_invocable_ris_nothrow_invocableis_nothrow_invocable_r (C++17)(C++17)(C++17)(C++17) 类型修改 remove_cvremove_constremove_volatile (C++11)(C++11)(C++11) add_cvadd_constadd_volatile (C++11)(C++11)(C++11) make_signed (C++11) make_unsigned (C++11) remove_reference (C++11) add_lvalue_referenceadd_rvalue_reference (C++11)(C++11) remove_pointer (C++11) add_pointer (C++11) remove_extent (C++11) remove_all_extents (C++11) 类型转换 aligned_storage (C++11)(deprecated in C++23) aligned_union (C++11)(deprecated in C++23) decay (C++11) remove_cvref (C++20) result_ofinvoke_result (C++11)(until C++20*)(C++17) conditional (C++11) common_type (C++11) common_reference (C++20) underlying_type (C++11) type_identity (C++20) enable_if (C++11) void_t (C++17)
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integer_sequence (C++14)

 

定义于头文件 <type_traits>
template< class T > struct is_scoped_enum;		(since C++23)

std::is_scoped_enum 是一个 UnaryTypeTrait。

检查 T 是否为作用域枚举类型。提供成员常量 value，如果 T 是作用域枚举类型，则 value 等于 true。否则，value 等于 false。

如果程序为 std::is_scoped_enum 或 std::is_scoped_enum_v 添加特化，则行为未定义。

模板参数

T

-

要检查的类型

辅助变量模板

template< class T > constexpr bool is_scoped_enum_v = is_scoped_enum<T>::value;		(since C++23)

继承自 std::integral_constant

成员常量

value [静态]

如果 T 是作用域枚举类型，则为 true，否则为 false (public static member constant)

成员函数

operator bool	将对象转换为 bool，返回 value (public member function)
operator() (C++14)	返回 value (public member function)

成员类型

类型	定义
value_type	bool
type	std::integral_constant<bool, value>

注解

特性测试 宏	值	Std	特性
__cpp_lib_is_scoped_enum	202011L	(C++23)	std::is_scoped_enum

可能的实现

namespace detail { void test_conversion(...); // selected when E is complete and scoped void test_conversion(int) = delete; // selected when E is complete and unscoped   template<class E> concept is_scoped_enum_impl = std::is_enum_v<E> && // checked first requires { detail::test_conversion(E{}); }; // ill-formed before overload resolution // when E is incomplete } // namespace detail   template<class T> struct is_scoped_enum : std::bool_constant<detail::is_scoped_enum_impl<T>> {};

示例

运行此代码

#include <type_traits>
 
static_assert(std::is_scoped_enum_v<int> == false);
 
class A {};
static_assert(std::is_scoped_enum_v<A> == false);
 
enum B { self_test = std::is_scoped_enum_v<B> };
static_assert(std::is_scoped_enum_v<B> == false);
static_assert(!self_test);
 
enum struct C { final, import, module };
static_assert(std::is_scoped_enum_v<C> == true);
 
enum class D : int { pre, post, override };
static_assert(std::is_scoped_enum_v<D> == true);
 
enum class E;
static_assert(std::is_scoped_enum_v<E> == true);
 
int main() {}

参见

is_integral (C++11)	检查类型是否为整型 (class template)
is_arithmetic (C++11)	检查类型是否为算术类型 (class template)
is_scalar (C++11)	检查类型是否为标量类型 (class template)
is_enum (C++11)	检查类型是否为枚举类型 (class template)