Defined in header <scoped_allocator> | ||
---|---|---|
template < class T, class... Args > void construct( T* p, Args&&... args ); | (1) | |
template< class T1, class T2, class... Args1, class... Args2 > void construct( std::pair<T1, T2>* p, std::piecewise_construct_t, std::tuple<Args1...> x, std::tuple<Args2...> y ); | (2) | |
template< class T1, class T2 > void construct( std::pair<T1, T2>* p ); | (3) | |
template< class T1, class T2, class U, class V > void construct( std::pair<T1, T2>* p, U&& x, V&& y ); | (4) | |
template< class T1, class T2, class U, class V > void construct( std::pair<T1, T2>* p, const std::pair<U, V>& xy ); | (5) | |
template< class T1, class T2, class U, class V > void construct( std::pair<T1, T2>* p, std::pair<U, V>&& xy ); | (6) |
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, determines the outermost allocator type OUTERMOST
: it is the type that would be returned by calling this->outer_allocator()
, and then calling the outer_allocator()
member function recursively on the result of this call until reaching the type that has no such member function. That type is the outermost allocator.
Then:
1) If std::uses_allocator<T, inner_allocator_type>::value==false
(the type T
does not use allocators) and if std::is_constructible<T, Args...>::value==true
, then calls.
std::allocator_traits<OUTERMOST>::construct( OUTERMOST(*this),
p,
std::forward<Args>(args)... );
Otherwise, if std::uses_allocator<T, inner_allocator_type>::value==true
(the type T
uses allocators, e.g. it is a container) and if std::is_constructible<T, std::allocator_arg_t, inner_allocator_type, Args...>::value==true
, then calls.
std::allocator_traits<OUTERMOST>::construct( OUTERMOST(*this),
p,
std::allocator_arg,
inner_allocator(),
std::forward<Args>(args)... );
Otherwise, std::uses_allocator<T, inner_allocator_type>::value==true
(the type T
uses allocators, e.g. it is a container) and if std::is_constructible<T, Args..., inner_allocator_type>::value==true
, then calls.
std::allocator_traits<OUTERMOST>::construct( OUTERMOST(*this),
p,
std::forward<Args>(args)...,
inner_allocator());
Otherwise, compilation error is issued because although std::uses_allocator<T>
claimed that T
is allocator-aware, it lacks either form of allocator-accepting constructors.
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 x
, unmodified. (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::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::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 (this also requires that all types in Args1... and Args2... are CopyConstructible
), constructs the pair p
in allocated storage by calling.
std::allocator_traits<OUTERMOST>::construct( OUTERMOST(*this),
p,
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 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)))
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::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.
See also
[static] | constructs an object in the allocated storage (function template) |
constructs an object in allocated storage (public member function of std::allocator ) |
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