std::meta::info

 

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Reflection library

Checking string literals is_string_literal Types info meta::exception access_context data_member_options member_offset operators Concepts reflection_range Promoting to static storage reflect_constant_string reflect_constant_array define_static_string define_static_array define_static_object Operator representations operator_of symbol_of u8symbol_of Names and locations has_identifier identifier_of u8identifier_of display_string_of u8display_string_of source_location_of Reflection queries ➜ Member accessibility queries is_accessible has_inaccessible_nonstatic_   data_members has_inaccessible_bases has_inaccessible_subobjects

Scope identification current_function current_class current_namespace Reflection member queries members_of bases_of static_data_members_of nonstatic_data_members_of      subobjects_of enumerators_of Reflection layout queries offset_of size_of alignment_of bit_size_of Annotation reflection annotations_of annotations_of_with_type Value extraction extract Reflection substitution can_substitute substitute Expression result reflection reflect_constant reflect_object reflect_function Class definition generation data_member_spec is_data_member_spec define_aggregate

Primary type categories is_void_type is_null_pointer_type is_integral_type is_floating_point_type is_array_type is_pointer_type is_lvalue_reference_type is_rvalue_reference_type is_member_object_pointer_type is_member_function_pointer_type      is_enum_type is_union_type is_class_type is_function_type is_reflection_type Composite type categories is_reference_type is_arithmetic_type is_fundamental_type is_object_type is_scalar_type is_compound_type is_member_pointer_type Type properties ➜ Type relations is_same_type is_base_of_type is_virtual_base_of_type is_convertible_type is_nothrow_convertible_type is_layout_compatible_type is_pointer_interconvertible_   base_of_type is_invocable_type is_invocable_r_type is_nothrow_invocable_type is_nothrow_invocable_r_type

Const-volatile modifications remove_const remove_volatile remove_cv add_const add_volatile add_cv Reference modifications remove_reference add_lvalue_reference add_rvalue_reference Sign modifications make_signed make_unsigned Array modifications remove_extent remove_all_extents Pointer modifications remove_pointer add_pointer Other transformations remove_cvref decay common_type common_reference underlying_type invoke_result unwrap_reference unwrap_ref_decay tuple_size tuple_element is_applicable_type is_nothrow_applicable_type apply_result variant_size variant_alternative type_order

 

Reflection types and queries

Reflection queries type_of object_of constant_of is_public is_protected is_private is_virtual is_pure_virtual is_override is_final is_deleted is_defaulted is_user_provided is_user_declared is_explicit is_noexcept is_bit_field is_enumerator is_annotation is_const is_volatile is_mutable_member is_lvalue_reference_qualified is_rvalue_reference_qualified has_static_storage_duration has_thread_storage_duration has_automatic_storage_duration      has_internal_linkage has_module_linkage has_external_linkage has_linkage has_c_language_linkage is_complete_type is_enumerable_type is_variable is_type is_namespace is_type_alias is_namespace_alias is_function is_conversion_function is_operator_function is_literal_operator is_special_member_function is_destructor

is_constructor is_default_constructor is_copy_constructor is_move_constructor is_assignment is_copy_assignment is_move_assignment is_function_parameter is_explicit_object_parameter has_default_argument is_vararg_function is_template is_function_template is_variable_template is_class_template is_alias_template is_conversion_function_template      is_operator_function_template is_literal_operator_template is_constructor_template is_concept is_value is_object is_structured_binding is_class_member is_namespace_member is_nonstatic_data_member is_static_member is_base has_default_member_initializer has_parent parent_of dealias has_template_arguments template_of template_arguments_of parameters_of variable_of return_type_of Type properties is_const_type is_volatile_type is_trivially_copyable_type is_standard_layout_type is_empty_type

is_polymorphic_type is_abstract_type is_final_type is_aggregate_type is_structural_type is_signed_type is_unsigned_type is_bounded_array_type is_unbounded_array_type is_scoped_enum_type is_constructible_type is_trivially_constructible_type is_nothrow_constructible_type is_default_constructible_type is_trivially_default_constructible_type is_nothrow_default_constructible_type is_copy_constructible_type is_trivially_copy_constructible_type is_nothrow_copy_constructible_type is_move_constructible_type is_trivially_move_constructible_type is_nothrow_move_constructible_type is_assignable_type is_trivially_assignable_type is_nothrow_assignable_type is_copy_assignable_type is_trivially_copy_assignable_type is_nothrow_copy_assignable_type is_move_assignable_type is_trivially_move_assignable_type is_nothrow_move_assignable_type is_swappable_with_type is_swappable_type is_nothrow_swappable_with_type is_nothrow_swappable_type is_destructible_type is_trivially_destructible_type is_nothrow_destructible_type is_implicit_lifetime_type has_virtual_destructor has_unique_object_representations reference_constructs_from_temporary reference_converts_from_temporary Type property queries rank extent

 

Defined in header <meta>
using info = decltype(^^::);		(since C++26)

std::meta::info is the type of reflection values. It is a distinct fundamental type. There exists a unique null reflection; every other reflection represents:

• a value of scalar type;
• an object of static storage duration;
• a variable;
• a structured binding;
• a function;
• a function parameter;
• an enumerator;
• an annotation;
• a type;
• a type alias;
• a class member;
• an unnamed bit-field;
• a class template;
• a function template;
• a variable template;
• an alias template;
• a concept;
• a namespace;
• a namespace alias;
• a direct base class relationship; or
• a data member description.

For the purpose of argument-dependent lookup, the namespace std::meta is an associated namespace of this type.

Values of type std::meta::info are equality-comparable. Note that a reflection of a type alias compares unequal to a reflection of the aliased type.

Example

Run this code

#include <meta>
#include <print>

// Obtain reflection object
constexpr std::meta::info r{^^int};

// Define a variable from reflection object “r”
constexpr typename [:r:] x{42};
static_assert(x == 42);

// std::meta::info objects are equality-comparable
static_assert(^^int == ^^int);
static_assert(^^int != ^^char);

// Reflection of type alias compares unequal to a reflection of the aliased type
using Int = int;
using INT = Int;
static_assert(^^int != ^^INT);

// Dealiasing can be used to reach to underlying type reflection
static_assert(^^int == std::meta::dealias(^^INT));

int main()
{
    std::print("{}\n", std::meta::display_string_of(^^int));
    std::print("{}\n", std::meta::display_string_of(dealias(^^INT))); // ADL
    std::print("{}\n", std::meta::display_string_of(^^Int));
    std::print("{}\n", std::meta::display_string_of(std::meta::info()));
}

Possible output:

int
int
Int {aka int}
<null reflection>

See also

• Reflection operator ^^
• Splice specifiers