std::polymorphic

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Compiler support
Freestanding and hosted
Language
Standard library
Standard library headers
Named requirements
Feature test macros(C++20)
Language support library
Concepts library(C++20)
Diagnostics library
Memory management library
Metaprogramming library(C++11)
General utilities library
Containers library
Iterators library
Ranges library(C++20)
Algorithms library
Strings library
Text processing library
Numerics library
Date and time library
Input/output library
Filesystem library(C++17)
Concurrency support library(C++11)
Execution control library(C++26)
Technical specifications
Symbols index
External libraries

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Memory management library

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)

Low level memory
management

operator newoperator new[]

operator deleteoperator delete[]

(C++11)

(C++11)

(C++17)

(C++20)

(C++17)

(C++11)

(C++11)

(C++11)

(until C++17*)

(C++11)

(C++17)

(C++26)

(C++26)

enable_shared_from_this

(C++11)

(C++11)

(C++11)

(C++23)

(C++23)

(C++11)

(C++20)

(C++11)

(C++11)

(C++20)

is_sufficiently_aligned

(C++26)

C Library

malloc
calloc
realloc

free
aligned_alloc (C++17)

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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)

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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.

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

Anstd::polymorphic object manages thelifetime of an owned object. The owned object is of typeT or any type (publicly and unambiguously) derived fromT. Anstd::polymorphic object can only have no owned object after it has been moved from, in this case it isvalueless .

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

If a program declares an explicit or partial specialization ofstd::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 anincomplete 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 ofstd::in_place_type_t a cv-qualified type
- If`Allocator` does not satisfy the requirements ofAllocator, the program is ill-formed.
- Ifstd::allocator_traits<Allocator>::value_type is not the same type as`T`, the program is ill-formed.

[edit]Nested types

Type	Definition
`value_type`	`T`
`allocator_type`	`Allocator`
`pointer`	typenamestd::allocator_traits<Allocator>::pointer
`const_pointer`	typenamestd::allocator_traits<Allocator>::const_pointer

[edit]Data members

Member	Description
`Allocatoralloc`	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]