| 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), provides the member constant value equal to true. Otherwise value is false.
Helper variable template
template< class T, class Alloc > constexpr bool uses_allocator_v = uses_allocator<T, Alloc>::value; | (since C++17) |
Inherited from std::integral_constant
Member constants
| value [static] | true if T uses allocator Alloc, false otherwise (public static member constant) |
Member functions
| operator bool | converts the object to bool, returns value (public member function) |
| operator() (C++14) | returns value (public member function) |
Member types
| Type | Definition |
|---|---|
value_type | bool |
type | std::integral_constant<bool, value> |
Specializations
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++11) | specializes the std::uses_allocator type trait (function template) |
specializes the std::uses_allocator type trait (function template) | |
| (C++11) | specializes the std::uses_allocator type trait (function template) |
specializes the std::uses_allocator type trait (class template specialization) | |
specializes the std::uses_allocator type trait (class template specialization) | |
specializes the std::uses_allocator type trait (class template specialization) |
Notes
This type trait is used by std::scoped_allocator_adaptor and may be used by custom allocators to determine whether the object 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.
See also
| (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) |
| std::experimental::uses_allocator_v
(library fundamentals TS) | variable template alias of std::uses_allocator::value (variable template) |
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