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.
template< class T, class Alloc > inline constexpr bool uses_allocator_v = uses_allocator<T, Alloc>::value; | (since C++17) |
| value
[static] | true if T uses allocator Alloc, false otherwise (public static member constant) |
| operator bool | converts the object to bool, returns value (public member function) |
| operator()
(C++14) | returns value (public member function) |
| Type | Definition |
|---|---|
value_type | bool |
type | std::integral_constant<bool, value> |
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:
T has a constructor which takes std::allocator_arg_t as the first argument, and Alloc as the second argument.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:
|
(C++11) | specializes the std::uses_allocator type trait (class template specialization) |
|
(C++17) | specializes the std::uses_allocator type trait (class template specialization) |
|
(C++11) | specializes the std::uses_allocator type trait (function template) |
|
(C++11) | specializes the std::uses_allocator type trait (function template) |
|
(C++11) | specializes the std::uses_allocator type trait (function template) |
|
(C++11) (until C++17) | specializes the std::uses_allocator type trait (class template specialization) |
|
(C++11) | specializes the std::uses_allocator type trait (class template specialization) |
|
(C++11)(until C++17) | specializes the std::uses_allocator type trait (class template specialization) |
This type trait is used by std::scoped_allocator_adaptor, std::tuple, std::variant, and std::pmr::polymorphic_allocator. It may also be used by custom allocators or wrapper types to determine whether the object or member being constructed is itself capable of using an allocator (e.g. is a container), in which case an allocator should be passed to its constructor.
|
(C++11) | an object of type std::allocator_arg_t used to select allocator-aware constructors (constant) |
|
(C++11) | tag type used to select allocator-aware constructor overloads (class) |
|
(C++11) | implements multi-level allocator for multi-level containers (class template) |
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