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Showing content from https://en.cppreference.com/w/cpp/language/../types/reference_converts_from_temporary.html below:

std::reference_converts_from_temporary - cppreference.com

template< class T, class U > struct reference_converts_from_temporary;

(since C++23)

Let V be std::remove_cv_t<U> if U is a scalar type or cv void, or U otherwise. If T is a reference type, and given a hypothetical expression e such that decltype(e) is V, the variable definition T ref = e; is well-formed and binds a temporary object to ref, then provides the member constant value equal to true. Otherwise, value is false.

If T is an lvalue reference type to a const- but not volatile-qualified object type or an rvalue reference type, both std::remove_reference_t<T> and std::remove_reference_t<U> shall be complete types, cv void, or an arrays of unknown bound; 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.

[edit] Helper variable template template< class T, class U > inline constexpr bool reference_converts_from_temporary_v = std::reference_converts_from_temporary<T, U>::value; (since C++23) Inherited from std::integral_constant Member constants true if T is a reference type, a U value can be bound to T in copy-initialization, and a temporary object would be bound to the reference, false otherwise
(public static member constant) Member functions converts the object to bool, returns value
(public member function) returns value
(public member function) Member types [edit] Notes

std::reference_converts_from_temporary can be used for rejecting some cases that always produce dangling references.

[edit] Example

#include <type_traits>
 
int main() {}
 
static_assert(
    std::reference_converts_from_temporary_v<int&&, int> == true &&
    std::reference_converts_from_temporary_v<const int&, int> == true &&
    std::reference_converts_from_temporary_v<int&&, int&&> == false &&
    std::reference_converts_from_temporary_v<const int&, int&&> == false &&
    std::reference_converts_from_temporary_v<int&&, long&&> == true &&
    std::reference_converts_from_temporary_v<int&&, long> == true);

[edit] See also checks if a type can be converted to the other type
(class template) [edit] invokes any Callable object with given arguments and possibility to specify return type(since C++23)
(function template) [edit] binds one or more arguments to a function object
(function template) [edit] calls the provided functor with the arguments held by one or more variants
(function template) [edit] constructs a new std::function instance
(public member function of std::function<R(Args...)>) [edit] constructs a new std::move_only_function object
(public member function of std::move_only_function) [edit] constructs the task object
(public member function of std::packaged_task<R(Args...)>) [edit]

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