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std::experi...::construct(3) C++ Standard Libary std::experi...::construct(3) NAME std::experimental::pmr::polymorphic_allocator::construct - std::experi- mental::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->re- source(), 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 allo- cator 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->re- source()), std::move(x)) 2c) if T1 is allocator-aware (std::uses_allocator<T1, memory_resource*>::value==true), and its constructor takes the allo- cator as the last argument (std::is_constructible<T1, Args1..., memory_re- source*>::value==true), then xprime is std::tuple_cat(std::move(x), std::make_tuple(this->re- source())). 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 al- located 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::tu- ple<>(), 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_tu- ple(std::forward<U>(x)), std::forward_as_tuple(std::forward<V>(y))) 5) Equivalent to construct(p, std::piecewise_construct, std::forward_as_tu- ple(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 allo- cator-aware object, such as std::vector, that was given a std::polymorphic_allo- cator 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>) http://cppreference.com 2022.07.31 std::experi...::construct(3)
NAME | Synopsis | Parameters | Return value | Notes | See also
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