std::pmr::polymorphic_allocator
Defined in header <memory_resource> |
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template< class T > class polymorphic_allocator; |
(since C++17) (until C++20) |
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template< class T = std::byte > class polymorphic_allocator; |
(since C++20) |
The class template std::pmr::polymorphic_allocator
is an Allocator which exhibits different allocation behavior depending upon the std::pmr::memory_resource
from which it is constructed. Since memory_resource
uses runtime polymorphism to manage allocations, different container instances with polymorphic_allocator
as their static allocator type are interoperable, but can behave as if they had different allocator types.
All specializations of polymorphic_allocator
meet the Allocator completeness requirements.
The polymorphic_allocator::construct
member function does uses-allocator construction, so that the elements of a container using a polymorphic_allocator
will use that same allocator for their own allocations. For example, a std::pmr::vector<std::pmr::string>
will use the same memory_resource
for the vector
's storage and each string
's storage.
Member types
Member type | definition |
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value_type |
T |
Member functions
Constructs a polymorphic_allocator (public member function) |
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(destructor)
(implicitly declared)
|
Implicitly declared destructor (public member function) |
operator=
[deleted]
|
Copy assignment operator is deleted (public member function) |
Public member functions |
|
Allocate memory (public member function) |
|
Deallocate memory (public member function) |
|
Constructs an object in allocated storage (public member function) |
|
(deprecated in C++20)
|
Destroys an object in allocated storage (public member function) |
(C++20)
|
Allocate raw aligned memory from the underlying resource (public member function) |
(C++20)
|
Free raw memory obtained from allocate_bytes (public member function) |
(C++20)
|
Allocates raw memory suitable for an object or an array (public member function) |
(C++20)
|
Frees raw memory obtained by allocate_object (public member function) |
(C++20)
|
Allocates and constructs an object (public member function) |
(C++20)
|
Destroys and deallocates an object (public member function) |
Create a new polymorphic_allocator for use by a container's copy constructor (public member function) |
|
Returns a pointer to the underlying memory resource (public member function) |
Non-member functions
(removed in C++20)
|
compare two polymorphic_allocator s (function) |
Notes
polymorphic_allocator
does not propagate on container copy assignment, move assignment, or swap. As a result, move assignment of a polymorphic_allocator
-using container can throw, and swapping two polymorphic_allocator
-using containers whose allocators do not compare equal results in undefined behavior.
Feature testing macro: __cpp_lib_polymorphic_allocator
.
See also
(C++17)
|
an abstract interface for classes that encapsulate memory resources (class) |
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