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std::pmr::p...::construct(3)   C++ Standard Libary  std::pmr::p...::construct(3)

NAME
     std::pmr::polymorphic_allocator::construct  - std::pmr::polymorphic_alloca-
     tor::construct

Synopsis
	template< class U, class... Args  >				     (1)
     (since C++17)
	void construct( U* p, Args&&... args );
	template< class T1, class T2, class... Args1, class... Args2 >

	void	      construct(	  std::pair<T1, 	 T2>*	      p,
     (since C++17)
			std::piecewise_construct_t,			     (2)
     (until C++20)
			std::tuple<Args1...> x,

			std::tuple<Args2...> y );
	template<  class  T1, class T2 >				     (3)
     (since C++17)
	void	   construct(	    std::pair<T1,	 T2>*	     p	      );
     (until C++20)
	template<  class  T1, class T2, class U, class V >		     (4)
     (since C++17)
	void   construct(   std::pair<T1,   T2>*   p,	U&&   x,   V&&	 y    );
     (until C++20)
	template<  class  T1, class T2, class U, class V >		     (5)
     (since C++17)
	void construct( std::pair<T1, T2>*  p,	const  std::pair<U,  V>&  xy  );
     (until C++20)
	template<  class  T1, class T2, class U, class V >		     (6)
     (since C++17)
	void  construct(  std::pair<T1,  T2>*  p,  std::pair<U,   V>&&	 xy   );
     (until C++20)
	template<  class  T1, class T2, class NonPair > 		     (7)
     (since C++17)
	void  construct(   std::pair<T1,   T2>*   p,   NonPair&&   non_pair   );
     (until C++20)

	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 down to the constructed
     object.

	1) Creates an object of the given type U by means of uses-allocator con-
     struction at
	the uninitialized memory location indicated by p, using *this as the al-
     locator.
	This overload participates in overload resolution only if  U  is  not  a
     specialization
	of std::pair.
	(until C++20)

     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,  polymorphic_allocator>::value==false)  and
     std::is_constructible<T1, Args1...>::value==true, then xprime is x, unmodi-
     fied.  2b)  if  T1  is  allocator-aware  (std::uses_allocator<T1,	polymor-
     phic_allocator>::value==true),  and  its constructor takes an allocator tag
     (std::is_constructible<T1,   std::allocator_arg_t,   polymorphic_allocator,
     Args1...>::value==true,   then   xprime   is   std::tuple_cat(std::make_tu-
     ple(std::allocator_arg, *this), std::move(x)).  2c)  if  T1  is  allocator-
     aware  (std::uses_allocator<T1,  polymorphic_allocator>::value==true),  and
     its constructor takes the allocator  as  the  last  argument  (std::is_con-
     structible<T1,  Args1..., polymorphic_allocator>::value==true), then xprime
     is std::tuple_cat(std::move(x),  std::make_tuple(*this)).	 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::piece-
     wise_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
     (until
											       C++20)
     construct(p,   std::piecewise_construct,	 std::forward_as_tuple(std::for-
     ward<U>(x)),
					    std::forward_as_tuple(std::for-
     ward<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::for-
     ward<U>(xy.first)),
					    std::forward_as_tuple(std::for-
     ward<V>(xy.second)))

     7) This overload participates in overload resolution only if given the  ex-
     position-only function template

     template<	class  A,  class B > void /*deduce-as-pair*/( const std::pair<A,
     B>& );

     , /*deduce-as-pair*/(non_pair) is ill-formed when considered as an unevalu-
     ated operand.  Equivalent to

     construct<T1, T2, T1, T2>(p, std::forward<NonPair>(non_pair));

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
	non_pair - non-pair argument to convert to pair for further construction

Return value
	(none)

Notes
	This  function	is called (through std::allocator_traits) by any alloca-
     tor-aware
	object, such as std::pmr::vector (or another std::vector that was  given
     a
	std::pmr::polymorphic_allocator as the allocator to use).

	Defect reports

	The  following	behavior-changing  defect  reports were applied retroac-
     tively to
	previously published C++ standards.

	   DR	 Applied to	    Behavior as  published		 Correct
     behavior
	LWG 2969 C++17	    uses-allocator construction passed	   passes *this
			    resource()
	LWG  2975  C++17      first overload is mistakenly used for  constrained
     to not accept
			    pair construction in some cases	   pairs
	LWG 3525 C++17	    no overload could handle non-pair	    reconstruct-
     ing overload
			    types convertible to pair		   added

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>)

http://cppreference.com 	   2024.06.10	    std::pmr::p...::construct(3)
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