From cppreference.com
template<classTo,classFrom>structreference_converts_from_temporary;(since C++23)Let V be std::remove_cv_t<From> if From is a scalar type or
void, or From otherwise. If To is a reference type, and given a hypothetical expression e such that decltype(e) is V, the variable definition Toref=e; is well-formed and
to ref, then provides the member constant value equal to true. Otherwise, value is false.
If To is an lvalue reference type to a const- but not volatile-qualified object type or an rvalue reference type, both std::remove_reference_t<To> and std::remove_reference_t<From> must be
,
void, or an
; otherwise the behavior is undefined.
If an instantiation of a template above depends, directly or indirectly, on an incomplete type, and that instantiation could yield a different result if that type were hypothetically completed, the behavior is undefined.
If the program adds specializations for std::reference_converts_from_temporary or std::reference_converts_from_temporary_v, the behavior is undefined.
Helper variable template
template<classTo,classFrom>constexprboolreference_converts_from_temporary_v=std::reference_converts_from_temporary<To,From>::value;(since C++23)Inherited from
Member constants
value
[static]
true if To is a reference type, a From value can be bound to To in copy-initialization, and a temporary object would be bound to the reference, false otherwise
(public static member constant)Member functions
operator bool
converts the object to bool, returns value
(public member function)operator()
(C++14)
returns value
(public member function)Member types
Type Definition value_typebooltypestd::integral_constant<bool,value>Notes
std::reference_converts_from_temporary can be used for rejecting some cases that always produce dangling references.
Example
Run this code
#include<type_traits>static_assert(""&&std::reference_converts_from_temporary_v<int&&,int>==true&&std::reference_converts_from_temporary_v<constint&,int>==true&&std::reference_converts_from_temporary_v<int&&,int&&>==false&&std::reference_converts_from_temporary_v<constint&,int&&>==false&&std::reference_converts_from_temporary_v<int&&,long&&>==true&&std::reference_converts_from_temporary_v<int&&,long>==true);intmain(){}See also
is_convertibleis_nothrow_convertible
(C++11)(C++20)
checks if a type can be converted to the other type
(class template)
(C++17)(C++23)
invokes any
object with given arguments and possibility to specify return type(since C++23)
(function template)
(C++11)
binds one or more arguments to a function object
(function template)
(C++17)
calls the provided functor with the arguments held by one or more variants
(function template)
constructs a new std::function instance
(public member function of std::function<R(Args...)>)
constructs a new std::move_only_function object
(public member function of std::move_only_function)
constructs the task object
(public member function of std::packaged_task<R(Args...)>)
reference_constructs_from_temporary
(C++23)
checks if a reference is bound to a temporary in
(class template)
reference_converts_from_temporary
(C++26)
checks if a reference is bound to a temporary in
(function)