[meta.reflection.names]

# 21 Metaprogramming library [[meta]](./#meta)

## 21.4 Reflection [[meta.reflection]](meta.reflection#names)

### 21.4.6 Reflection names and locations [meta.reflection.names]

[🔗](#lib:has_identifier)

`consteval bool has_identifier(info r);
`

[1](#1)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/meta.tex#L3673)

*Returns*: 

- [(1.1)](#1.1)

  If r represents an entity
 that has a typedef name for linkage purposes ([[dcl.typedef]](dcl.typedef "9.2.4 The typedef specifier")),
 then true[.](#1.1.sentence-1)

- [(1.2)](#1.2)

  Otherwise, if r represents an unnamed entity,
 then false[.](#1.2.sentence-1)

- [(1.3)](#1.3)

  Otherwise, if r represents a class type,
 then !has_template_arguments(r)[.](#1.3.sentence-1)

- [(1.4)](#1.4)

  Otherwise, if r represents a function,
 then true if has_template_arguments(r) is false and the function is not a
 constructor,
 destructor,
 operator function, or
 conversion function[.](#1.4.sentence-1)
  Otherwise, false[.](#1.4.sentence-2)

- [(1.5)](#1.5)

  Otherwise, if r represents a template,
 then true if r does not represent a
 constructor template,
 operator function template,
 or conversion function template[.](#1.5.sentence-1)
  Otherwise, false[.](#1.5.sentence-2)

- [(1.6)](#1.6)

  Otherwise, if r represents the ith parameter of a function F that is an (implicit or explicit) specialization of a templated function T and the ith parameter of the instantiated declaration of T whose template arguments are those of F would be instantiated from a pack,
 then false[.](#1.6.sentence-1)

- [(1.7)](#1.7)

  Otherwise, if r represents the parameter P of a function F,
 then let S be the set of declarations,
 ignoring any explicit instantiations,
 that precede some point in the evaluation context
 and that declare either F or a templated function
 of which F is a specialization; true if
  * [(1.7.1)](#1.7.1)

there is a declaration D in S that introduces a name N for either P or the parameter corresponding to P in the templated function that D declares and

  * [(1.7.2)](#1.7.2)

no declaration in S does so using any name other than N[.](#1.7.sentence-1)

   Otherwise, false[.](#1.7.sentence-2)
  [*Example [1](#example-1)*: void fun(int);constexpr std::meta::info r = parameters_of(^^fun)[0];static_assert(!has_identifier(r));

    void fun(int x);static_assert(has_identifier(r));

    void fun(int x);static_assert(has_identifier(r));

    void poison() {void fun(int y);}static_assert(!has_identifier(r)); — *end example*]

- [(1.8)](#1.8)

  Otherwise, if r represents a variable,
 then false if the declaration of that variable
 was instantiated from a function parameter pack[.](#1.8.sentence-1)
  Otherwise, !has_template_arguments(r)[.](#1.8.sentence-2)

- [(1.9)](#1.9)

  Otherwise, if r represents a structured binding,
 then false if the declaration of that structured binding
 was instantiated from a structured binding pack[.](#1.9.sentence-1)
  Otherwise, true[.](#1.9.sentence-2)

- [(1.10)](#1.10)

  Otherwise, if r represents a type alias,
 then !has_template_arguments(r)[.](#1.10.sentence-1)

- [(1.11)](#1.11)

  Otherwise, if r represents an
 enumerator,
 non-static-data member,
 namespace, or
 namespace alias,
 then true[.](#1.11.sentence-1)

- [(1.12)](#1.12)

  Otherwise, if r represents a direct base class relationship,
 then has_identifier(type_of(r))[.](#1.12.sentence-1)

- [(1.13)](#1.13)

  Otherwise, r represents a data member description (T,N,A,W,NUA) ([[class.mem.general]](class.mem.general "11.4.1 General")); true if N is not ⊥[.](#1.13.sentence-1)
  Otherwise, false[.](#1.13.sentence-2)

[🔗](#lib:identifier_of)

`consteval string_view identifier_of(info r);
consteval u8string_view u8identifier_of(info r);
`

[2](#2)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/meta.tex#L3782)

Let E be UTF-8 for u8identifier_of,
and otherwise the ordinary literal encoding[.](#2.sentence-1)

[3](#3)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/meta.tex#L3786)

*Returns*: An ntmbs, encoded with E,
determined as follows:

- [(3.1)](#3.1)

  If r represents an entity with a typedef name for linkage purposes,
 then that name[.](#3.1.sentence-1)

- [(3.2)](#3.2)

  Otherwise, if r represents a literal operator or literal operator template,
 then the [*ud-suffix*](lex.ext#nt:ud-suffix "5.13.9 User-defined literals [lex.ext]") of the operator or operator template[.](#3.2.sentence-1)

- [(3.3)](#3.3)

  Otherwise, if r represents the parameter P of a function F,
 then let S be the set of declarations,
 ignoring any explicit instantiations,
 that precede some point in the evaluation context
 and that declare either F or a templated function of which F is a specialization;
 the name that was introduced by a declaration in S for the parameter corresponding to P[.](#3.3.sentence-1)

- [(3.4)](#3.4)

  Otherwise, if r represents an entity,
 then the identifier introduced by the declaration of that entity[.](#3.4.sentence-1)

- [(3.5)](#3.5)

  Otherwise, if r represents a direct base class relationship,
 then identifier_of(type_of(r)) or u8identifier_of(type_of(r)),
 respectively[.](#3.5.sentence-1)

- [(3.6)](#3.6)

  Otherwise, r represents a data member description (T,N,A,W,NUA) ([[class.mem.general]](class.mem.general "11.4.1 General"));
 a string_view or u8string_view, respectively,
 containing the identifier N[.](#3.6.sentence-1)

[4](#4)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/meta.tex#L3820)

*Throws*: meta​::​exception unlesshas_identifier(r) is true and the identifier that would be returned (see above)
is representable by E[.](#4.sentence-1)

[🔗](#lib:display_string_of)

`consteval string_view display_string_of(info r);
consteval u8string_view u8display_string_of(info r);
`

[5](#5)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/meta.tex#L3836)

*Returns*: Animplementation-definedstring_view or u8string_view, respectively[.](#5.sentence-1)

[6](#6)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/meta.tex#L3842)

*Recommended practice*: Where possible,
implementations should return a string
suitable for identifying the represented construct[.](#6.sentence-1)

[🔗](#lib:source_location_of)

`consteval source_location source_location_of(info r);
`

[7](#7)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/meta.tex#L3855)

*Returns*: If r represents
a value,
a type other than a class type or an enumeration type,
the global namespace, or
a data member description,
then source_location{}[.](#7.sentence-1)

Otherwise, animplementation-definedsource_location value[.](#7.sentence-2)

[8](#8)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/meta.tex#L3867)

*Recommended practice*: If r represents an entity with a definition
that is reachable from the evaluation context,
a value corresponding to a definition should be returned[.](#8.sentence-1)