std::uses_allocator (3) - Linux Man Pages
Defined in header <memory>
template< class T, class Alloc > struct uses_allocator; (since C++11)
If T has a member typedef allocator_type which is convertible from Alloc
or is an alias of std::experimental::erased_type
(library fundamentals TS), the member constant value is true. Otherwise value is false.
Helper variable template
template< class T, class Alloc > (since C++17)
inline constexpr bool uses_allocator_v = uses_allocator<T, Alloc>::value;
Inherited from std::integral_constant
value true if T uses allocator Alloc, false otherwise
operator bool (public member function)
operator() returns value
type std::integral_constant<bool, value>
There are three conventions of passing an allocator alloc to a constructor of some type T:
* if T does not use a compatible allocator (std::uses_allocator_v<T, Alloc> is false), then alloc is ignored.
* otherwise, std::uses_allocator_v<T, Alloc> is true, and
* As a special case, std::pair is treated as a uses-allocator type even though std::uses_allocator is false for pairs (unlike e.g. std::tuple): see pair-specific overloads of
The utility functions std::make_obj_using_allocator, and std::uninitialized_construct_using_allocator may be used to explicitly create an object following the above protocol, and std::uses_allocator_construction_args can be used to prepare the argument list that matches the flavor of uses-allocator construction expected by the type. (since C++20)
Custom specializations of the type trait std::uses_allocator are allowed for types that do not have the member typedef allocator_type but satisfy one of the following two requirements:
1) T has a constructor which takes std::allocator_arg_t as the first argument, and Alloc as the second argument.
2) T has a constructor which takes Alloc as the last argument.
In the above, Alloc is a type that satisfies Allocator
or is a pointer type convertible to std::experimental::pmr::memory_resource*
(library fundamentals TS).
The following specializations are already provided by the standard library:
std::uses_allocator<std::tuple> specializes the std::uses_allocator type trait
std::uses_allocator<std::queue> specializes the std::uses_allocator type trait
std::uses_allocator<std::priority_queue> specializes the std::uses_allocator type trait
std::uses_allocator<std::stack> specializes the std::uses_allocator type trait
std::uses_allocator<std::function> specializes the std::uses_allocator type trait