std::experimental::pmr::polymorphic_allocator::construct(3)

NAME
std::experimental::pmr::polymorphic_allocator::construct - std::experimental::pmr::polymorphic_allocator::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, (2) (library fundamentals TS)
                   std::piecewise_construct_t,
                   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 >
   void construct( std::pair<T1, T2>* p, const (5) (library fundamentals TS)
   std::pair<U, V>& xy );
   template< class T1, class T2, class U, class V >
   void construct( std::pair<T1, T2>* p, std::pair<U, (6) (library fundamentals TS)
   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
   [static] (function template)
   construct constructs an object in allocated storage
   (until C++20) (public member function of std::allocator<T>)

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