std::uses_allocator
STD：：用途[医]分配器
| Defined in header | | |
|---|---|---|
| template< class T, class Alloc > struct uses_allocator; | | (since C++11) |
如果T有一个成员类型allocator_type可转换的Alloc或者是std::experimental::erased_type%28库基础要素TS%29，成员常量value是true.否则value是false...
辅助变量模板
| template< class T, class Alloc > inline constexpr bool uses_allocator_v = uses_allocator | | (since C++17) |
|---|
继承自STD：积分[医]常量
成员常数
| value static | true if T uses allocator Alloc, false otherwise (public static member constant) |
|---|
成员函数
| operator bool | converts the object to bool, returns value (public member function) |
|---|---|
| operator() (C++14) | returns value (public member function) |
成员类型
| Type | Definition |
|---|---|
| value_type | bool |
| type | std::integral_constant<bool, value> |
专门性
类型特征的自定义专门化std::uses_allocator对于不具有成员ty对联f的类型，则允许使用allocator_type但满足以下两项要求之一：
1%29T具有一个构造函数，该构造函数将std::allocator_arg_t作为第一个论点Alloc作为第二个论点。
2%29T具有一个构造函数，该构造函数将Alloc作为最后的论据。
在上面，Alloc是满足以下条件的类型Allocator或者是指针类型可转换为std::experimental::pmr::memory_resource*%28库基础要素TS%29。
标准库已经提供了以下专门化：
| std::uses_allocator | specializes the std::uses_allocator type trait (class template specialization) |
|---|---|
| std::uses_allocator<std::variant> (C++17) | specializes the std::uses_allocator type trait (class template specialization) |
| std::uses_allocator<std::queue> (C++11) | specializes the std::uses_allocator type trait (function template) |
| std::uses_allocator<std::priority_queue> (C++11) | specializes the std::uses_allocator type trait (function template) |
| std::uses_allocator<std::stack> (C++11) | specializes the std::uses_allocator type trait (function template) |
| std::uses_allocator<std::function> (C++11) (until C++17) | specializes the std::uses_allocator type trait (class template specialization) |
| std::uses_allocator<std::promise> (C++11) | specializes the std::uses_allocator type trait (class template specialization) |
| std::uses_allocator<std::packaged_task> (C++11)(until C++17) | specializes the std::uses_allocator type trait (class template specialization) |
注记
使用此类型特征的std::scoped_allocator_adaptor，，，std::tuple，，，std::variant，和std::pmr::polymorphic_allocator它还可以被自定义分配器或包装器类型使用，以确定正在构造的对象或成员本身是否能够使用分配器%28例如。是容器%29，在这种情况下，应将分配器传递给其构造函数。
另见
| allocator_arg (C++11) | an object of type std::allocator_arg_t used to select allocator-aware constructors (constant) |
|---|---|
| allocator_arg_t (C++11) | tag type used to select allocator-aware constructor overloads (class) |
| scoped_allocator_adaptor (C++11) | implements multi-level allocator for multi-level containers (class template) |
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