std::experimental::pmr::polymorphic_allocator::construct (3) Linux Manual Page

std::experimental::pmr::polymorphic_allocator<T>::construct – std::experimental::pmr::polymorphic_allocator<T>::construct

Synopsis

template <class U, class... Args>
(1)(library fundamentals TS)

    void construct(U *p, Args &&...args);

template <class T1, class T2, class... Args1, class... Args2>

void construct(std::pair<T1, T2> *p,

               std::piecewise_construct_t, (2)(library fundamentals TS)

                                               std::tuple<Args1...>
                                                   x,

               std::tuple<Args2...> y);

template <class T1, class T2>
(3)(library fundamentals TS)

    void construct(std::pair<T1, T2> *p);

template <class T1, class T2, class U, class V>
(4)(library fundamentals TS)

    void construct(std::pair<T1, T2> *p, U &&x, V &&y);

template <class T1, class T2, class U, class V>
(5)(library fundamentals TS)

    void construct(std::pair<T1, T2> *p, const std::pair<U, V> &xy);

template <class T1, class T2, class U, class V>
(6)(library fundamentals TS)

    void construct(std::pair<T1, T2> *p, std::pair<U, V> &&xy);

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 constructs an object in the allocated storage
                      (function template)
[static]
construct constructs an object in allocated storage
                      (public member function of std::allocator<T>)
(deprecated in C++17)
(removed in C++20)