std::experimental::pmr::polymorphic_allocator::construct

 

C++

Language

Standard library headers

Concepts

Utilities library

Strings library

Containers library

Algorithms library

Iterators library

Numerics library

Input/output library

Localizations library

Regular expressions library (C++11)

Atomic operations library (C++11)

Thread support library (C++11)

Filesystem library (C++17)

Technical Specifications

 

Library fundamentals

experimental::optional

experimental::any

experimental::basic_string_view

experimental::sample

experimental::shared_ptr

experimental::weak_ptr

experimental::apply

experimental::invocation_type experimental::raw_invocation_type

experimental::search

experimental::default_searcher experimental::make_default_searcher

experimental::boyer_moore_searcher experimental::make_boyer_moore_searcher

experimental::boyer_moore_horspool_searcher experimental::make_boyer_moore_horspool_searcher

type-erased and polymorphic allocators

variable templates for type traits

 

Polymorphic allocator library

polymorphic_allocator

convenience aliases for containers using polymorphic_allocator

Memory resource classes

memory_resource

synchronized_pool_resource

unsynchronized_pool_resource

monotonic_buffer_resource

resource_adaptor

Global memory resources

new_delete_resource

null_memory_resource

get_default_resource

set_default_resource

Type-erased allocator support for existing classes

function

packaged_task

promise

 

std::experimental::pmr::polymorphic_allocator

Member functions

polymorphic_allocator::polymorphic_allocator

polymorphic_allocator::operator=

polymorphic_allocator::allocate

polymorphic_allocator::deallocate

polymorphic_allocator::construct

polymorphic_allocator::destroy

polymorphic_allocator::select_on_container_copy_construction

polymorphic_allocator::resource

Non-member functions

operator==operator!=

 

template < class U, class... Args > void construct( U* p, Args&&... args );	(1)	(library fundamentals TS)
template< class T1, class T2, class... Args1, class... Args2 > void construct( std::pair<T1, T2>* p,                 std::piecewise_construct_t,                 std::tuple<Args1...> x,                 std::tuple<Args2...> y );	(2)	(library fundamentals TS)
template< class T1, class T2 > void construct( std::pair<T1, T2>* p );	(3)	(library fundamentals TS)
template< class T1, class T2, class U, class V > void construct( std::pair<T1, T2>* p, U&& x, V&& y );	(4)	(library fundamentals TS)
template< class T1, class T2, class U, class V > void construct( std::pair<T1, T2>* p, const std::pair<U, V>& xy );	(5)	(library fundamentals TS)
template< class T1, class T2, class U, class V > void construct( std::pair<T1, T2>* p, std::pair<U, V>&& xy );	(6)	(library fundamentals TS)

Constructs an object in allocated, but not initialized storage pointed to by p the provided constructor arguments. If the object is of type that itself uses allocators, or if it is std::pair, passes this->resource() down to the constructed object.

1) If std::uses_allocator<U, memory_resource*>::value==false (the type U does not use allocators) and std::is_constructible<U, Args...>::value==true, then constructs the object as if by ::new((void *) p) U(std::forward<Args>(args)... );.

Otherwise, if std::uses_allocator<U, memory_resource*>::value==true (the type U uses allocators, e.g. it is a container) and std::is_constructible<U, std::allocator_arg_t, memory_resource*, Args...>::value==true, then constructs the object as if by ::new((void *) p) U(std::allocator_arg, this->resource(), std::forward<Args>(args)... );.

Otherwise, if std::uses_allocator<U, memory_resource*>::value==true (the type U uses allocators, e.g. it is a container) and std::is_constructible<U, Args..., memory_resource*>::value==true, then constructs the object as if by ::new((void *) p) U(std::forward<Args>(args)..., this->resource());.

Otherwise, the program is ill-formed.

2) First, if either T1 or T2 is allocator-aware, modifies the tuples x and y to include this->resource(), resulting in the two new tuples xprime and yprime, according to the following three rules:

2a) if T1 is not allocator-aware (std::uses_allocator<T1, memory_resource*>::value==false) and std::is_constructible<T1, Args1...>::value==true, then xprime is x, unmodified.

2b) if T1 is allocator-aware (std::uses_allocator<T1, memory_resource*>::value==true), and its constructor takes an allocator tag (std::is_constructible<T1, std::allocator_arg_t, memory_resource*, Args1...>::value==true, then xprime is std::tuple_cat(std::make_tuple(std::allocator_arg, this->resource()), std::move(x))

2c) if T1 is allocator-aware (std::uses_allocator<T1, memory_resource*>::value==true), and its constructor takes the allocator as the last argument (std::is_constructible<T1, Args1..., memory_resource*>::value==true), then xprime is std::tuple_cat(std::move(x), std::make_tuple(this->resource())).

2d) Otherwise, the program is ill-formed.

Same rules apply to T2 and the replacement of y with yprime.

Once xprime and yprime are constructed, constructs the pair p in allocated storage as if by ::new((void *) p) pair<T1, T2>(std::piecewise_construct, std::move(xprime), std::move(yprime));

3) Equivalent to construct(p, std::piecewise_construct, std::tuple<>(), std::tuple<>()), that is, passes the memory resource on to the pair's member types if they accept them.

4) Equivalent to

construct(p, std::piecewise_construct, std::forward_as_tuple(std::forward<U>(x)),
                                       std::forward_as_tuple(std::forward<V>(y)))

5) Equivalent to

construct(p, std::piecewise_construct, std::forward_as_tuple(xy.first),
                                       std::forward_as_tuple(xy.second))

6) Equivalent to

construct(p, std::piecewise_construct, std::forward_as_tuple(std::forward<U>(xy.first)),
                                       std::forward_as_tuple(std::forward<V>(xy.second)))

Parameters

p	-	pointer to allocated, but not initialized storage
args...	-	the constructor arguments to pass to the constructor of T
x	-	the constructor arguments to pass to the constructor of T1
y	-	the constructor arguments to pass to the constructor of T2
xy	-	the pair whose two members are the constructor arguments for T1 and T2

Return value

(none)

Notes

This function is called (through std::allocator_traits) by any allocator-aware object, such as std::vector, that was given a std::polymorphic_allocator as the allocator to use. Since memory_resource* implicitly converts to polymorphic_allocator, the memory resource pointer will propagate to any allocator-aware subobjects using polymorphic allocators.

See also

construct [static]	constructs an object in the allocated storage (function template)
construct	constructs an object in allocated storage (public member function of std::allocator)