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std::polymorphic

Defined in header `<memory>`
template< class T, class Allocator = std::allocator<T> > class polymorphic;	(1)	(since C++26)
namespace pmr { template< class T > using polymorphic = std::polymorphic<T, std::pmr::polymorphic_allocator<T>>; }	(2)	(since C++26)

1) std::polymorphic is a wrapper containing dynamically-allocated object of possibly different types with value-like semantics.

An std::polymorphic object manages the lifetime of an owned object. The owned object is of type T or any type (publicly and unambiguously) derived from T. An std::polymorphic object can only have no owned object after it has been moved from, in this case it is valueless .

Every object of type std::polymorphic<T, Allocator> uses an object of type Allocator to allocate and free storage for the owned object as needed.

If a program declares an explicit or partial specialization of std::polymorphic, the behavior is undefined.

[edit] Template parameters

T	-	the type of the owned object
Allocator	-	the type of the associated allocator
Type requirements
-`T` may be an incomplete type.
-If `T` is one of the following types, the program is ill-formed: a non-object type an array type std::in_place_t a specialization of std::in_place_type_t a cv-qualified type
-If `Allocator` does not satisfy the requirements of Allocator, the program is ill-formed.
-If std::allocator_traits<Allocator>::value_type is not the same type as `T`, the program is ill-formed.

[edit] Nested types

[edit] Data members

Member	Description
`Allocator` `alloc`	the asociated allocator (exposition-only member object*)

[edit] Member functions

(constructor)	constructs the `polymorphic` object (public member function) [edit]
(destructor)	destroys the owned value, if there is one (public member function) [edit]
operator=	assigns contents (public member function) [edit]
Observers
operator->operator*	accesses the owned value (public member function) [edit]
valueless_after_move	checks if the `polymorphic` is valueless (public member function) [edit]
get_allocator	returns the associated allocator (public member function) [edit]
Modifiers
swap	exchanges the contents (public member function) [edit]

[edit] Non-member functions

[edit] Notes

Feature-test macro	Value	Std	Feature
`__cpp_lib_polymorphic`	`202502L`	(C++26)	`std::polymorphic`

[edit] Example

[edit] See also

(C++26)

a wrapper containing dynamically-allocated object with value-like semantics
(class template) [edit]

std::polymorphic - cppreference.com

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