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)

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.

Contents 1 Template parameters 2 Nested types 3 Data members 4 Member functions 4.1 Observers 4.2 Modifiers 5 Non-member functions 6 Notes 7 Example 8 See also

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.

Nested types

Type	Definition
value_type	T
allocator_type	Allocator
pointer	typename std:: allocator_traits < Allocator > :: pointer
const_pointer	typename std:: allocator_traits < Allocator > :: const_pointer

Data members

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

Member functions

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

Non-member functions

std::swap (std::polymorphic) (C++26)

specializes the std::swap algorithm (function template)

Notes

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

Example

This section is incomplete Reason: no example

See also

indirect (C++26)

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