std::scoped_allocator_adaptor::construct(3)

NAME
std::scoped_allocator_adaptor::construct - std::scoped_allocator_adaptor::construct

Synopsis
   Defined in header <scoped_allocator>
   template < class T, class... Args > (1)
   void construct( T* p, Args&&... args );
   template< class T1, class T2, class... Args1, class... Args2 >
   void construct( std::pair<T1, T2>* p,
   std::piecewise_construct_t, (2) (until C++20)
   std::tuple<Args1...> x,
   std::tuple<Args2...> y );
   template< class T1, class T2 > (3) (until C++20)
   void construct( std::pair<T1, T2>* p );
   template< class T1, class T2, class U, class V > (4) (until C++20)
   void construct( std::pair<T1, T2>* p, U&& x, V&& y );
   template< class T1, class T2, class U, class V > (5) (until C++20)
   void construct( std::pair<T1, T2>* p, const std::pair<U, V>& xy );
   template< class T1, class T2, class U, class V > (6) (until C++20)
   void construct( std::pair<T1, T2>* p, std::pair<U, V>&& xy );
   template< class T1, class T2, class NonPair > (7) (until C++20)
   void construct( std::pair<T1, T2>* p, NonPair&& non_pair );
   Constructs an object in allocated, but not initialized storage pointed to by p using
   OuterAllocator and the provided constructor arguments. If the object is of type that
   itself uses allocators, or if it is std::pair, passes InnerAllocator down to the
   constructed object.
   First, retrieve the outermost allocator OUTERMOST by calling
   this->outer_allocator(), and then calling the outer_allocator() member function
   recursively on the result of this call until reaching an allocator that has no such
   member function.
   Define OUTERMOST_ALLOC_TRAITS(x) as
   std::allocator_traits<std::remove_reference_t<decltype(OUTERMOST(x))>>
   1) Creates an object of the given type T by means of uses-allocator construction at
   the uninitialized memory location indicated by p, using OUTERMOST as the allocator.
   After adjustment for uses-allocator convention expected by T's constructor, calls
   OUTERMOST_ALLOC_TRAITS(*this)::construct.
   This overload participates in overload resolution only if U is not a (until
   specialization of std::pair. C++20)
   Equivalent to
   std::apply(
       [p,this](auto&&... newargs) {
           OUTERMOST_ALLOC_TRAITS(*this)::construct(
               OUTERMOST(*this), p, std::forward<decltype(newargs)>(newargs)...); (since
       }, C++20)
       std::uses_allocator_construction_args(
           inner_allocator(),
           std::forward<Args>(args)...
       )
   );
  2) First, if either T1 or T2 is allocator-aware, modifies the tuples x and y to
  include the appropriate inner allocator, 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,
  inner_allocator_type>::value==false, then xprime is
  std::tuple<Args1&&...>(std::move(x)). (it is also required that
  std::is_constructible<T1, Args1...>::value==true)
  2b) if T1 is allocator-aware (std::uses_allocator<T1,
  inner_allocator_type>::value==true), and its constructor takes an allocator tag
  (std::is_constructible<T1, std::allocator_arg_t, inner_allocator_type&,
  Args1...>::value==true), then xprime is
  std::tuple_cat(std::tuple<std::allocator_arg_t, inner_allocator_type&>(
                      std::allocator_arg, inner_allocator()
                 ),
                 std::tuple<Args1&&...>(std::move(x)))
  2c) if T1 is allocator-aware (std::uses_allocator<T1,
  inner_allocator_type>::value==true), and its constructor takes the allocator as
  the last argument (std::is_constructible<T1, Args1...,
  inner_allocator_type&>::value==true), then xprime is
  std::tuple_cat(std::tuple<Args1&&...>(std::move(x)),
  std::tuple<inner_allocator_type&>(inner_allocator())).
  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 by calling
  std::allocator_traits<O>::construct( OUTERMOST,
                        p,
                        std::piecewise_construct,
                        std::move(xprime), (until
                        std::move(yprime)); C++20)
  3) Equivalent to construct(p, std::piecewise_construct, std::tuple<>(),
  std::tuple<>()), that is, passes the inner allocator 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)))
  7) This overload participates in overload resolution only if given the
  exposition-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 unevaluated
  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 allocator-aware
   object, such as std::vector, that was given a std::scoped_allocator_adaptor as the
   allocator to use. Since inner_allocator is itself an instance of
   std::scoped_allocator_adaptor, this function will also be called when the
   allocator-aware objects constructed through this function start constructing their
   own members.
  Defect reports
   The following behavior-changing defect reports were applied retroactively to
   previously published C++ standards.
      DR Applied to Behavior as published Correct behavior
                       first overload is mistakenly used constrained to not accept
   LWG 2975 C++11 for pair construction in some pairs
                       cases
   P0475R1 C++11 pair piecewise construction may transformed to tuples of
                       copy the arguments references to avoid copy
   LWG 3525 C++11 no overload could handle non-pair reconstructing overload added
                       types convertible to pair

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>)