The C++ Extensions for Reflection, ISO/IEC TS 23619:2021, specifies modifications to the core language and defines new components for the C++ standard library listed on this page.
The Reflection TS is based on the C++20 standard (except that the definition of concepts are specified in the style of Concepts TS).
[edit] Core language changes [edit] reflexpr-specifierA reflexpr-specifier is of form reflexpr ( reflexpr-operand ), and specifies a meta-object type (see below).
reflexpr-operand can be one of following:
:: (1) type-id (2) nested-name-specifier(optional) namespace-name (3) id-expression (4) ( expression ) (5) function-call-expression (6) functional-type-conv-expression (7)
where function-call-expression is
postfix-expression( expression-list(optional) )
and functional-type-conv-expression are following sorts of expressions which perform explict cast:
simple-type-specifier( expression-list(optional) ) (1) typename-specifier ( expression-list(optional) ) (2) simple-type-specifier braced-init-list (3) typename-specifier braced-init-list (4)
The operand to the reflexpr-specifier shall be a type, namespace, enumerator, variable, data member, function parameter, captured entity, function-call-expression or functional-type-conv-expression, and parenthesized expression. reflexpr(::) reflects the global namespace.
For a reflexpr-operand of form ( expression ), the expression shall be a (possibly multi-parenthesized) function-call-expression or functional-type-conv-expression.
If an unparenthesized operand can be treated as either a type-id or a functional-type-conv-expression, then it is treated as a type-id. Parenthesizes can be used for disambiguation between function-style cast and a type-id. For example, given a class type X with default constructor, reflexpr(X()) reflects the function type X(), and reflexpr((X())) reflects the expression X().
If the operand designates both an alias and a class name, the type represented by the reflexpr-specifier reflects the alias and satisfies reflect::Alias.
If the operand designates a name whose declaration is enclosed in a block scope and the named entity is neither captured nor a function parameter, the program is ill-formed.
[edit] Meta-object typesA meta-object type is an unnamed, incomplete namespace-scope class type. A type satisfies the concept reflect::Object if and only if it is a meta-object type. Meta-object types may satisfy other concepts, depending on the operand to reflexpr.
It is unspecified whether repeatedly applying reflexpr to the same operand yields the same type or a different type. If a meta-object type reflects an incomplete class type, certain type transformations cannot be applied.
A meta-object type allows inspection of some properties of the operand to reflexpr through type traits or type transformations on it.
If the postfix-expression of the function-call-expression is of class type, i.e. e in the function-call-expression e(args) is of class type, then the user-defined conversion function of the type of the postfix-expression (e) shall not be used.
If postfix-expression is not of class type, it shall name a function that is the unique result of overload resolution.
struct Functor
{
void operator()(int) const;
using fptr_t = void(*)(std::nullptr_t);
operator fptr_t() const;
};
using Meta0 = reflexpr(Functor{}(0)); // OK
// using Meta1 = reflexpr(Functor{}(nullptr)); // error: conversion function used[edit]
An alias is a name introduced by a typedef declaration, an alias-declaration, or a using-declaration.
An entity or alias B is reflection-related to an entity or alias A if
A and B are the same entity or alias,A is a variable or enumerator and B is the type of A,A is an enumeration and B is the underlying type of A,A is a class and B is a member or base class of A,A is a non-template alias that designates the entity B,A is not the global namespace and B is an enclosing class or namespace of A,A is the parenthesized expression ( B ),A is a lambda capture of the closure type B,A is the closure type of the lambda capture B,B is the type specified by the functional-type-conv-expression A,B is the function selected by overload resolution for a function-call-expression A,B is the return type, a parameter type, or function type of the function A, orB is reflection-related to an entity or alias X and X is reflection-related to A.Reflection-relation relationship is reflexive and transitive, but not symmetric.
Informally speaking, the case that B is reflection-related to A means that B participates in the declaration or definition of A.
Zero or more successive applications of type transformations that yield meta-object types to the type denoted by a reflexpr-specifier enable inspection of entities and aliases that are reflection-related to the operand; such a meta-object type is said to reflect the respective reflection-related entity or alias.
struct X;
struct B
{
using X = ::X;
typedef X Y;
};
struct D : B
{
using B::Y;
};
// ::X, but not B::X or B::Y is reflection-related to D::Y[edit] Miscellaneous
reflexpr operand is not considered to be an unevaluated operand.T is odr-used by the specialization std::experimental::reflect::get_pointer<T>, as if by taking the address of an id-expression nominating the function or variable.__cpp_reflection
(reflection TS)
a value of at least 201902 indicates that the Reflection TS is supportedRecordMember, Enumerator, or Variable, or reflects a namespace other than the global namespace
get_base_classes
Object operations checks if two meta-object types reflect the same entity or alias
ObjectSequence operations obtains the size of a meta-object sequence
Named operations checks if the reflected entity or alias is unnamed
Alias operations obtains the meta-object type reflecting the associated entity of the reflected alias
Type operations obtains the meta-object type reflecting the type of the reflected entity or alias
ScopeMember operations obtains the meta-object type reflecting the scope of the reflected entity or alias
Base operations obtains the meta-object type reflecting the base class in the given base class relationship
RecordMember and Base operations checks if the reflected member or base class is public
Record operations obtains a meta-object sequence type whose elements reflect public, accessible, or all data members of the reflected class
Enum operations checks whether the reflected enumeration is scoped
Variable operations obtains the value of the reflected variable which is a constant expression
FunctionParameter operations checks whether the reflected parameter has a default argument
Callable operations obtains a meta-object sequence type whose elements reflects the parameters of the reflected function
Variable and Callable operations checks if the reflected variable or function is constexpr
Namespace and Callable operations checks whether the reflected namespace or function is inline
ParenthesizedExpression operations obtains the meta-object type reflecting the unparenthesized expression of the reflected parethesized expression
FunctionCallExpression operations obtains the meta-object type reflecting the function in the reflected function-call-expression
FunctionalTypeConversion operations obtains the meta-object type reflecting the constructor in reflected functional-type-conv-expression
Variable and Function operations get the address of the reflected variable or function, or the pointer-to-member value to the reflected non-static member
MemberFunction operations checks if the reflected member function is declared with const, volatile, &, or && qualifier respectively
Record and MemberFunction operations checks if the reflected class or member function is marked with final
Variable and MemberFunction operations checks if the reflected variable is of static storage duration, or the reflected member function is static
SpecialMemberFunction operations checks if the reflected special member function is implicitly declared
Constructor and ConversionOperator operations checks if the reflected constructor or conversion function is declared with explicit
MemberFunction and Destructor operations checks if the reflected member function is virtual
Lambda operations obtains a meta-object sequence type whose elements reflect the captures of the reflected closure type
= or & respectively
operator() of the reflected closure type is declared with const
LambdaCapture operations checks if the reflected lambda capture is explicitly captured
__cpp_lib_reflection
(reflection TS)
a value of at least 201902 indicates that the support library of the Reflection TS is supportedThe following table lists that whether a meta-object type reflecting an operand satisfies concepts introduced by the Reflection TS.
Categoryreflexpr operands Satisfied concepts Type class-name designating a union reflect::Union class-name designating a closure type reflect::Lambda class-name designating a non-union class reflect::Record enum-name reflect::Enum template type-parameter reflect::Type, reflect::Alias decltype-specifier reflect::Type, reflect::Alias type-name introduced by a using-declaration reflect::Type, reflect::Alias, reflect::ScopedMember any other typedef-name reflect::Type, reflect::Alias any other type-id reflect::Type Namespace namespace-alias reflect::Namespace, reflect::Alias the global namespace reflect::GlobalScope any other namespace reflect::Namespace Expression the name of a data member reflect::Variable the name of a variable reflect::Variable the name of an enumerator reflect::Enumerator the name of a function parameter reflect::FunctionParameter the name of a captured entity reflect::LambdaCapture parenthesized expression reflect::ParenthesizedExpression function-call-expression reflect::FunctionCallExpression functional-type-conv-expression reflect::FunctionalTypeConversion
If the operand of the form id-expression is a constant expression, the type specified by the reflexpr-specifier also satisfies reflect::Constant.
If the reflexpr-operand designates a class member, the type represented by the reflexpr-specifier also satisfies reflect::RecordMember.
RetroSearch is an open source project built by @garambo | Open a GitHub Issue
Search and Browse the WWW like it's 1997 | Search results from DuckDuckGo
HTML:
3.2
| Encoding:
UTF-8
| Version:
0.7.4