std::polymorphic

 

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voidify (exposition only*) Allocators allocator allocator_traits (C++11) allocation_result (C++23) scoped_allocator_adaptor (C++11) pmr::polymorphic_allocator (C++17) allocator_arg (C++11) uses_allocator (C++11) uses_allocator_construction_args (C++20) make_obj_using_allocator (C++20) uninitialized_construct_using_allocator (C++20) Uninitialized memory algorithms uninitialized_copy uninitialized_fill uninitialized_move (C++17) uninitialized_copy_n (C++11) uninitialized_fill_n uninitialized_move_n (C++17) construct_at (C++20) uninitialized_default_construct (C++17) uninitialized_value_construct (C++17) destroy (C++17) uninitialized_default_construct_n (C++17) uninitialized_value_construct_n (C++17) destroy_n (C++17) destroy_at (C++17) Constrained uninitialized memory algorithms ranges::uninitialized_copy (C++20) ranges::uninitialized_fill (C++20) ranges::uninitialized_move (C++20) ranges::uninitialized_copy_n (C++20)  ranges::uninitialized_fill_n (C++20) ranges::uninitialized_move_n (C++20) ranges::construct_at (C++20) ranges::uninitialized_default_construct (C++20) ranges::uninitialized_value_construct (C++20) ranges::destroy (C++20) ranges::uninitialized_default_construct_n (C++20)  ranges::uninitialized_value_construct_n (C++20) ranges::destroy_n (C++20) ranges::destroy_at (C++20) Memory resources pmr::memory_resource (C++17) pmr::get_default_resource (C++17) pmr::set_default_resource (C++17) pmr::new_delete_resource (C++17) pmr::pool_options (C++17) pmr::null_memory_resource (C++17) pmr::synchronized_pool_resource (C++17) pmr::unsynchronized_pool_resource (C++17) pmr::monotonic_buffer_resource (C++17) Explicit lifetime management start_lifetime_as (C++23) start_lifetime_as_array (C++23) Types for composite class design indirect (C++26) polymorphic (C++26) Uninitialized storage (until C++20) raw_storage_iterator (until C++20*) get_temporary_buffer (until C++20*) return_temporary_buffer (until C++20*) Garbage collector support (until C++23) declare_reachable (C++11)(until C++23) declare_no_pointers (C++11)(until C++23) pointer_safety (C++11)(until C++23) undeclare_reachable (C++11)(until C++23) undeclare_no_pointers (C++11)(until C++23) get_pointer_safety (C++11)(until C++23)

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std::polymorphic

Member functions

polymorphic::polymorphic

polymorphic::~polymorphic

polymorphic::operator=

Observers

polymorphic::operator->polymorphic::operator*

polymorphic::valueless_after_move

polymorphic::get_allocator

Modifiers

polymorphic::swap

Non-member functions

swap(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.

2) std::pmr::polymorphic is an alias template that uses a polymorphic allocator.

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

(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

See also

indirect (C++26)

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