From Jason Turner

[meta.reflection.names]

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C++ Weekly: Ep 503

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+ ### Reflection names and locations <a id="meta.reflection.names">[[meta.reflection.names]]</a>
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+
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+ ``` cpp
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+ consteval bool has_identifier(info r);
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+ ```
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+
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+ *Returns:*
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+
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+ - If `r` represents an entity that has a typedef name for linkage
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+ purposes [[dcl.typedef]], then `true`.
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+ - Otherwise, if `r` represents an unnamed entity, then `false`.
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+ - Otherwise, if `r` represents a class type, then
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+ `!has_template_arguments(r)`.
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+ - Otherwise, if `r` represents a function, then `true` if
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+ `has_template_arguments(r)` is `false` and the function is not a
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+ constructor, destructor, operator function, or conversion function.
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+ Otherwise, `false`.
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+ - Otherwise, if `r` represents a template, then `true` if `r` does not
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+ represent a constructor template, operator function template, or
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+ conversion function template. Otherwise, `false`.
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+ - Otherwise, if `r` represents the iᵗʰ parameter of a function F that is
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+ an (implicit or explicit) specialization of a templated function T and
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+ the iᵗʰ parameter of the instantiated declaration of T whose template
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+ arguments are those of F would be instantiated from a pack, then
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+ `false`.
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+ - Otherwise, if `r` represents the parameter P of a function F, then let
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+ S be the set of declarations, ignoring any explicit instantiations,
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+ that precede some point in the evaluation context and that declare
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+ either F or a templated function of which F is a specialization;
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+ `true` if
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+ - there is a declaration D in S that introduces a name N for either P
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+ or the parameter corresponding to P in the templated function that D
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+ declares and
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+ - no declaration in S does so using any name other than N.
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+
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+ Otherwise, `false`.
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+ \[*Example 1*:
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+ void fun(int);
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+ constexpr std::meta::info r = parameters_of(^^fun)[0];
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+ static_assert(!has_identifier(r));
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+
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+ void fun(int x);
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+ static_assert(has_identifier(r));
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+
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+ void fun(int x);
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+ static_assert(has_identifier(r));
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+
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+ void poison() {
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+ void fun(int y);
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+ }
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+ static_assert(!has_identifier(r));
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+
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+ — *end example*]
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+ - Otherwise, if `r` represents a variable, then `false` if the
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+ declaration of that variable was instantiated from a function
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+ parameter pack. Otherwise, `!has_template_arguments(r)`.
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+ - Otherwise, if `r` represents a structured binding, then `false` if the
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+ declaration of that structured binding was instantiated from a
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+ structured binding pack. Otherwise, `true`.
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+ - Otherwise, if `r` represents a type alias, then
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+ `!has_template_arguments(r)`.
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+ - Otherwise, if `r` represents an enumerator, non-static-data member,
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+ namespace, or namespace alias, then `true`.
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+ - Otherwise, if `r` represents a direct base class relationship, then
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+ `has_identifier(type_of(r))`.
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+ - Otherwise, `r` represents a data member description
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+ (T, N, A, W, *NUA*)[[class.mem.general]]; `true` if N is not $\bot$.
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+ Otherwise, `false`.
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+
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+ ``` cpp
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+ consteval string_view identifier_of(info r);
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+ consteval u8string_view u8identifier_of(info r);
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+ ```
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+
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+ Let E be UTF-8 for `u8identifier_of`, and otherwise the ordinary literal
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+ encoding.
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+
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+ *Returns:* An NTMBS, encoded with E, determined as follows:
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+
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+ - If `r` represents an entity with a typedef name for linkage purposes,
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+ then that name.
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+ - Otherwise, if `r` represents a literal operator or literal operator
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+ template, then the *ud-suffix* of the operator or operator template.
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+ - Otherwise, if `r` represents the parameter P of a function F, then let
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+ S be the set of declarations, ignoring any explicit instantiations,
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+ that precede some point in the evaluation context and that declare
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+ either F or a templated function of which F is a specialization; the
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+ name that was introduced by a declaration in S for the parameter
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+ corresponding to P.
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+ - Otherwise, if `r` represents an entity, then the identifier introduced
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+ by the declaration of that entity.
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+ - Otherwise, if `r` represents a direct base class relationship, then
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+ `identifier_of(type_of(r))` or `u8identifier_of(type_of(r))`,
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+ respectively.
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+ - Otherwise, `r` represents a data member description
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+ (T, N, A, W, NUA)[[class.mem.general]]; a `string_view` or
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+ `u8string_view`, respectively, containing the identifier N.
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+
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+ *Throws:* `meta::exception` unless `has_identifier(r)` is `true` and the
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+ identifier that would be returned (see above) is representable by E.
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+
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+ ``` cpp
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+ consteval string_view display_string_of(info r);
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+ consteval u8string_view u8display_string_of(info r);
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+ ```
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+
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+ *Returns:* An *implementation-defined* `string_view` or `u8string_view`,
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+ respectively.
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+
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+ *Recommended practice:* Where possible, implementations should return a
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+ string suitable for identifying the represented construct.
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+
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+ ``` cpp
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+ consteval source_location source_location_of(info r);
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+ ```
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+
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+ *Returns:* If `r` represents a value, a type other than a class type or
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+ an enumeration type, the global namespace, or a data member description,
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+ then `source_location{}`. Otherwise, an *implementation-defined*
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+ `source_location` value.
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+
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+ *Recommended practice:* If `r` represents an entity with a definition
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+ that is reachable from the evaluation context, a value corresponding to
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+ a definition should be returned.
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+