depish/cppdraft_translate
1
0
Fork 0
Code Issues Pull Requests Actions Packages Projects Releases Wiki Activity
Files
043225d523e821bfa89efb15f5074f0465fb7edf
cppdraft_translate/cppdraft/expr/reflect.md
Leonov Artur (Depish) 043225d523 Init
2025-10-25 03:02:53 +03:00

220 lines
13 KiB
Markdown
Raw Blame History

This file contains invisible Unicode characters

This file contains invisible Unicode characters that are indistinguishable to humans but may be processed differently by a computer. If you think that this is intentional, you can safely ignore this warning. Use the Escape button to reveal them.

[expr.reflect]
# 7 Expressions [[expr]](./#expr)
## 7.6 Compound expressions [[expr.compound]](expr.compound#expr.reflect)
### 7.6.2 Unary expressions [[expr.unary]](expr.unary#expr.reflect)
#### 7.6.2.10 The reflection operator [expr.reflect]
[reflect-expression:](#nt:reflect-expression "7.6.2.10 The reflection operator [expr.reflect]")
^^ ::
^^ [*reflection-name*](#nt:reflection-name "7.6.2.10 The reflection operator [expr.reflect]")
^^ [*type-id*](dcl.name#nt:type-id "9.3.2 Type names [dcl.name]")
^^ [*id-expression*](expr.prim.id.general#nt:id-expression "7.5.5.1 General [expr.prim.id.general]")
[reflection-name:](#nt:reflection-name "7.6.2.10 The reflection operator [expr.reflect]")
[*nested-name-specifier*](expr.prim.id.qual#nt:nested-name-specifier "7.5.5.3 Qualified names [expr.prim.id.qual]")opt [*identifier*](lex.name#nt:identifier "5.11 Identifiers [lex.name]")
[*nested-name-specifier*](expr.prim.id.qual#nt:nested-name-specifier "7.5.5.3 Qualified names [expr.prim.id.qual]") template [*identifier*](lex.name#nt:identifier "5.11 Identifiers [lex.name]")
[1](#1)
[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/expressions.tex#L6637)
The unary ^^ operator,
called the [*reflection operator*](#def:operator,reflection "7.6.2.10 The reflection operator [expr.reflect]"),
yields a prvalue of type std​::​meta​::​info ([[basic.fundamental]](basic.fundamental "6.9.2 Fundamental types"))[.](#1.sentence-1)
[*Note [1](#note-1)*:
This document places no restriction on representing, by reflections,
constructs not described by this document or
using the names of such constructs
as operands of [*reflect-expression*](#nt:reflect-expression "7.6.2.10 The reflection operator [expr.reflect]")*s*[.](#1.sentence-2)
— *end note*]
[2](#2)
[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/expressions.tex#L6648)
The component names of a [*reflection-name*](#nt:reflection-name "7.6.2.10 The reflection operator [expr.reflect]") are those of its [*nested-name-specifier*](expr.prim.id.qual#nt:nested-name-specifier "7.5.5.3 Qualified names [expr.prim.id.qual]") (if any) and
its [*identifier*](lex.name#nt:identifier "5.11 Identifiers [lex.name]")[.](#2.sentence-1)
The terminal name of a [*reflection-name*](#nt:reflection-name "7.6.2.10 The reflection operator [expr.reflect]") of the form[*nested-name-specifier*](expr.prim.id.qual#nt:nested-name-specifier "7.5.5.3 Qualified names [expr.prim.id.qual]") template [*identifier*](lex.name#nt:identifier "5.11 Identifiers [lex.name]") shall denote a template[.](#2.sentence-2)
[3](#3)
[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/expressions.tex#L6656)
A [*reflect-expression*](#nt:reflect-expression "7.6.2.10 The reflection operator [expr.reflect]") is parsed as
the longest possible sequence of tokens
that could syntactically form a [*reflect-expression*](#nt:reflect-expression "7.6.2.10 The reflection operator [expr.reflect]")[.](#3.sentence-1)
An unparenthesized [*reflect-expression*](#nt:reflect-expression "7.6.2.10 The reflection operator [expr.reflect]") that represents a template shall not be followed by <[.](#3.sentence-2)
[*Example [1](#example-1)*: static_assert(std::meta::is_type(^^int())); // ^^ applies to the type-id int()template<bool> struct X {};consteval bool operator<(std::meta::info, X<false>) { return false; }consteval void g(std::meta::info r, X<false> xv) { r == ^^int && true; // error: ^^ applies to the [*type-id*](dcl.name#nt:type-id "9.3.2 Type names [dcl.name]") int&& r == ^^int & true; // error: ^^ applies to the type-id int& r == (^^int) && true; // OK r == ^^int &&&& true; // error: int &&&& is not a valid [*type-id*](dcl.name#nt:type-id "9.3.2 Type names [dcl.name]")^^X < xv; // error: [*reflect-expression*](#nt:reflect-expression "7.6.2.10 The reflection operator [expr.reflect]") that represents a template is followed by <(^^X) < xv; // OK^^X<true> < xv; // OK} — *end example*]
[4](#4)
[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/expressions.tex#L6680)
A [*reflect-expression*](#nt:reflect-expression "7.6.2.10 The reflection operator [expr.reflect]") of the form ^^​::​ represents the global namespace[.](#4.sentence-1)
[5](#5)
[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/expressions.tex#L6684)
If a [*reflect-expression*](#nt:reflect-expression "7.6.2.10 The reflection operator [expr.reflect]") R matches
the form ^^[*reflection-name*](#nt:reflection-name "7.6.2.10 The reflection operator [expr.reflect]"),
it is interpreted as such;
the [*identifier*](lex.name#nt:identifier "5.11 Identifiers [lex.name]") is looked up and
the representation of R is determined as follows:
- [(5.1)](#5.1)
If lookup finds a declaration
that replaced a [*using-declarator*](namespace.udecl#nt:using-declarator "9.10 The using declaration [namespace.udecl]") during a single search ([[basic.lookup.general]](basic.lookup.general "6.5.1 General"), [[namespace.udecl]](namespace.udecl "9.10 The using declaration")),R is ill-formed[.](#5.1.sentence-1)
[*Example [2](#example-2)*: struct A { struct S {}; };struct B : A { using A::S; };constexpr std::meta::info r1 = ^^B::S; // error: A​::​S found through [*using-declarator*](namespace.udecl#nt:using-declarator "9.10 The using declaration [namespace.udecl]")struct C : virtual B { struct S {}; };struct D : virtual B, C {};
D::S s; // OK, names C​::​S per [[class.member.lookup]](class.member.lookup "6.5.2 Member name lookup")constexpr std::meta::info r2 = ^^D::S; // OK, result C​::​S not found through [*using-declarator*](namespace.udecl#nt:using-declarator "9.10 The using declaration [namespace.udecl]") — *end example*]
- [(5.2)](#5.2)
Otherwise, if lookup finds a namespace alias ([[namespace.alias]](namespace.alias "9.9.3 Namespace alias")),R represents that namespace alias[.](#5.2.sentence-1)
For any other [*namespace-name*](namespace.def.general#nt:namespace-name "9.9.2.1 General [namespace.def.general]"),R represents the denoted namespace[.](#5.2.sentence-2)
- [(5.3)](#5.3)
Otherwise, if lookup finds a namespace ([[basic.namespace]](basic.namespace "9.9 Namespaces")),R represents that namespace[.](#5.3.sentence-1)
- [(5.4)](#5.4)
Otherwise, if lookup finds a concept ([[temp.concept]](temp.concept "13.7.9 Concept definitions")),R represents the denoted concept[.](#5.4.sentence-1)
- [(5.5)](#5.5)
Otherwise, if lookup finds a template ([[temp.names]](temp.names "13.3 Names of template specializations")),
the representation of R is determined as follows:
* [(5.5.1)](#5.5.1)
If lookup finds an injected-class-name ([[class.pre]](class.pre "11.1 Preamble")), then:
+
[(5.5.1.1)](#5.5.1.1)
If the [*reflection-name*](#nt:reflection-name "7.6.2.10 The reflection operator [expr.reflect]") is of the form[*nested-name-specifier*](expr.prim.id.qual#nt:nested-name-specifier "7.5.5.3 Qualified names [expr.prim.id.qual]") template [*identifier*](lex.name#nt:identifier "5.11 Identifiers [lex.name]"),
then R represents the class template named by the injected-class-name[.](#5.5.1.1.sentence-1)
+
[(5.5.1.2)](#5.5.1.2)
Otherwise, the injected-class-name shall be unambiguous
when considered as a [*type-name*](dcl.type.simple#nt:type-name "9.2.9.3 Simple type specifiers [dcl.type.simple]") andR represents the class template specialization so named[.](#5.5.1.2.sentence-1)
* [(5.5.2)](#5.5.2)
Otherwise, if lookup finds an overload set,
that overload set shall contain only
declarations of a unique function template F;R represents F[.](#5.5.2.sentence-1)
* [(5.5.3)](#5.5.3)
Otherwise, if lookup finds
a class template, variable template, or alias template,R represents that template[.](#5.5.3.sentence-1)
[*Note [2](#note-2)*:
Lookup never finds a partial or explicit specialization[.](#5.5.3.sentence-2)
— *end note*]
- [(5.6)](#5.6)
Otherwise, if lookup finds a type alias A,R represents the underlying entity of A if A was introduced by the declaration of a template parameter;
otherwise, R represents A[.](#5.6.sentence-1)
- [(5.7)](#5.7)
Otherwise, if lookup finds a class or an enumeration,R represents the denoted type[.](#5.7.sentence-1)
- [(5.8)](#5.8)
Otherwise, if lookup finds a class member of an anonymous union ([[class.union.anon]](class.union.anon "11.5.2 Anonymous unions")), R represents that class member[.](#5.8.sentence-1)
- [(5.9)](#5.9)
Otherwise,
the [*reflection-name*](#nt:reflection-name "7.6.2.10 The reflection operator [expr.reflect]") shall be an [*id-expression*](expr.prim.id.general#nt:id-expression "7.5.5.1 General [expr.prim.id.general]") I and R is ^^I (see below)[.](#5.9.sentence-1)
[6](#6)
[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/expressions.tex#L6764)
A [*reflect-expression*](#nt:reflect-expression "7.6.2.10 The reflection operator [expr.reflect]") R of the form^^[*type-id*](dcl.name#nt:type-id "9.3.2 Type names [dcl.name]") represents an entity determined as follows:
- [(6.1)](#6.1)
If the [*type-id*](dcl.name#nt:type-id "9.3.2 Type names [dcl.name]") designates
a placeholder type ([[dcl.spec.auto.general]](dcl.spec.auto.general "9.2.9.7.1 General")),R is ill-formed[.](#6.1.sentence-1)
- [(6.2)](#6.2)
Otherwise, if the [*type-id*](dcl.name#nt:type-id "9.3.2 Type names [dcl.name]") names a type alias
that is a specialization of an alias template ([[temp.alias]](temp.alias "13.7.8 Alias templates")),R represents that type alias[.](#6.2.sentence-1)
- [(6.3)](#6.3)
Otherwise, R represents the type denoted by the [*type-id*](dcl.name#nt:type-id "9.3.2 Type names [dcl.name]")[.](#6.3.sentence-1)
[7](#7)
[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/expressions.tex#L6781)
A [*reflect-expression*](#nt:reflect-expression "7.6.2.10 The reflection operator [expr.reflect]") R of the form^^[*id-expression*](expr.prim.id.general#nt:id-expression "7.5.5.1 General [expr.prim.id.general]") represents an entity determined as follows:
- [(7.1)](#7.1)
If the [*id-expression*](expr.prim.id.general#nt:id-expression "7.5.5.1 General [expr.prim.id.general]") denotes
* [(7.1.1)](#7.1.1)
a variable declared by
an [*init-capture*](expr.prim.lambda.capture#nt:init-capture "7.5.6.3 Captures [expr.prim.lambda.capture]") ([[expr.prim.lambda.capture]](expr.prim.lambda.capture "7.5.6.3 Captures")),
* [(7.1.2)](#7.1.2)
a function-local predefined variable ([[dcl.fct.def.general]](dcl.fct.def.general "9.6.1 General")),
* [(7.1.3)](#7.1.3)
a local parameter introduced by
a [*requires-expression*](expr.prim.req.general#nt:requires-expression "7.5.8.1 General [expr.prim.req.general]") ([[expr.prim.req]](expr.prim.req "7.5.8 Requires expressions")), or
* [(7.1.4)](#7.1.4)
a local entity E ([[basic.pre]](basic.pre "6.1 Preamble")) for which a lambda scope intervenes
between the point at which E was introduced and R,
then R is ill-formed[.](#7.1.sentence-1)
- [(7.2)](#7.2)
Otherwise, if the [*id-expression*](expr.prim.id.general#nt:id-expression "7.5.5.1 General [expr.prim.id.general]") denotes an overload set S,
overload resolution for the expression &S with no target
shall select a unique function ([[over.over]](over.over "12.3 Address of an overload set"));R represents that function[.](#7.2.sentence-1)
- [(7.3)](#7.3)
Otherwise, if the [*id-expression*](expr.prim.id.general#nt:id-expression "7.5.5.1 General [expr.prim.id.general]") denotes
a variable, structured binding, enumerator, or non-static data member,R represents that entity[.](#7.3.sentence-1)
- [(7.4)](#7.4)
Otherwise, R is ill-formed[.](#7.4.sentence-1)
[*Note [3](#note-3)*:
This includes [*unqualified-id*](expr.prim.id.unqual#nt:unqualified-id "7.5.5.2 Unqualified names [expr.prim.id.unqual]")*s* that name a constant template parameter and[*pack-index-expression*](expr.prim.pack.index#nt:pack-index-expression "7.5.5.4 Pack indexing expression [expr.prim.pack.index]")*s*[.](#7.4.sentence-2)
— *end note*]
The [*id-expression*](expr.prim.id.general#nt:id-expression "7.5.5.1 General [expr.prim.id.general]") of
a [*reflect-expression*](#nt:reflect-expression "7.6.2.10 The reflection operator [expr.reflect]") is an unevaluated operand ([[expr.context]](expr.context "7.2.3 Context dependence"))[.](#7.sentence-2)
[*Example [3](#example-3)*: template<typename T> void fn() requires (^^T != ^^int);template<typename T> void fn() requires (^^T == ^^int);template<typename T> void fn() requires (sizeof(T) == sizeof(int));
constexpr std::meta::info a = ^^fn<char>; // OKconstexpr std::meta::info b = ^^fn<int>; // error: ambiguousconstexpr std::meta::info c = ^^std::vector; // OKtemplate<typename T>struct S {static constexpr std::meta::info r = ^^T; using type = T;};static_assert(S<int>::r == ^^int);static_assert(^^S<int>::type != ^^int);
typedef struct X {} Y;typedef struct Z {} Z;constexpr std::meta::info e = ^^Y; // OK, represents the type alias Yconstexpr std::meta::info f = ^^Z; // OK, represents the type alias Z, not the type ([[basic.lookup.general]](basic.lookup.general "6.5.1 General")) — *end example*]
Reference in New Issue View Git Blame Copy Permalink