std::meta::annotations_of

 

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Checking string literals is_string_literal Helper types info tuple_size tuple_element is_applicable_type is_nothrow_applicable_type      apply_result variant_size variant_alternative type_order exception Promoting to static storage reflect_constant_string reflect_constant_array define_static_string define_static_array define_static_object Operator representations operators 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 ➜ Access control context access_context

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 Annotation reflection annotations_of annotations_of_with_type Value extraction extract Reflection substitution reflection_range can_substitute substitute Expression result reflection reflect_constant reflect_object reflect_function Class definition generation data_member_options 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

 

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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_c_language_linkage has_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_constructor is_default_constructor is_copy_constructor

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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_default_constructible_type is_copy_constructible_type is_move_constructible_type is_assignable_type is_copy_assignable_type is_move_assignable_type is_swappable_with_type is_swappable_type is_destructible_type is_trivially_constructible_type is_trivially_default_constructible_type is_trivially_copy_constructible_type is_trivially_move_constructible_type is_trivially_assignable_type is_trivially_copy_assignable_type is_trivially_move_assignable_type is_trivially_destructible_type is_nothrow_constructible_type is_nothrow_default_constructible_type is_nothrow_copy_constructible_type is_nothrow_move_constructible_type is_nothrow_assignable_type is_nothrow_copy_assignable_type is_nothrow_move_assignable_type is_nothrow_swappable_with_type is_nothrow_swappable_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>
consteval std::vector<std::meta::info> annotations_of( std::meta::info item );		(since C++26)

Returns a vector containing reflections of annotations that apply to the entity represented by item.

If item represents a function parameter P of a function F, then let S be the set of declarations, ignoring any explicit instantiations, that are reachable from a point in the evaluation context and that declare either F or a templated function of which F is a specialization, the result contains reflections of all the annotations that apply to P in every declaration in S.

If item represents a direct base class relationship, the result contains reflections of all the annotations that apply to the corresponding base-specifier.

For any two reflections R1 and R2 in the returned vector, if the annotation represented by R1 precedes the annotation represented by R2, then R1 is before R2 in the vector. If R1 and R2 represent annotations from the same translation unit T, any elements between R1 and R2 in the returned vector represent annotations from T. The order is otherwise unspecified.

Parameters

item

-

a reflection value

Return value

a vector containing reflections of annotations that apply to what item represents.

Exceptions

Throws std::meta::exception unless item represents one of the following:

• type
• type alias
• variable
• function
• function parameter
• namespace
• enumerator
• direct base class relationship
• non-static data member

Example

Run this code

#include <meta>
#include <print>

template<class T>
struct [[=42]] D {};

constexpr std::meta::info a1 = std::meta::annotations_of(^^D<int>)[0];
constexpr std::meta::info a2 = std::meta::annotations_of(^^D<char>)[0];
static_assert(a1 != a2);
static_assert(std::meta::constant_of(a1) == std::meta::constant_of(a2));

[[=1]] int x, y;
static_assert(std::meta::annotations_of(^^x)[0] == std::meta::annotations_of(^^y)[0]);

int main()
{
    [[=3.14]] typedef int var;
    typedef int var [[=42]];

    static constexpr auto annotations =
        std::define_static_array(std::meta::annotations_of(^^var));
    template for (constexpr auto ann : annotations) {
        std::println("{}", [:std::meta::constant_of(ann):]);
    }
}

Output:

3.14
42

See also

annotations_of_with_type (C++26)	obtains the annotations that apply to the reflected entity and have the specified type (function)
is_annotation (C++26)	checks if reflection represents an annotation (function)
constant_of (C++26)	obtains a reflection of the constant value of the reflected entity (function)
type_of (C++26)	obtains a reflection of the type of the reflected entity (function)