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std::polymorphic - cppreference.com

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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.

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

constructs the polymorphic object
(public member function) [edit]
destroys the owned value, if there is one
(public member function) [edit]
assigns contents
(public member function) [edit]
Observers
accesses the owned value
(public member function) [edit]
checks if the polymorphic is valueless
(public member function) [edit]
returns the associated allocator
(public member function) [edit]
Modifiers
exchanges the contents
(public member function) [edit]

Non-member functions

Notes

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

Example

See also

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