C++ 概念： Allocator
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封装内存分配和释放策略.
原文：
Encapsulates memory allocation and deallocation strategy.
每一个标准库组件，可能需要分配或释放存储，从
std::string，std::vector，和每一个容器除了std::array，以std::shared_ptrstd::function，通过Allocator：满足以下要求的类类型的对象.....原文：
Every standard library component that may need to allocate or release storage, from
std::string, std::vector, and every container except std::array, to std::shared_ptr and std::function, does so through an Allocator: an object of a class type that satisfies the following requirements.有些要求是可选的：模板std::allocator_traits提供的默认实现所有可选的要求，和所有的标准库容器和其他分配器感知类访问的分配器通过
std::allocator_traits，而不是直接.原文：
Some requirements are optional: the template std::allocator_traits supplies the default implementations for all optional requirements, and all standard library containers and other allocator-aware classes access the allocator through
std::allocator_traits, not directly.[编辑] 要求
鉴于
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B，相同类型U分配器 -
ptr，allocator_traits<A>::pointer类型的值，通过调用allocator_traits<A>::allocate()原文：ptr, a value of typeallocator_traits<A>::pointer, obtained by calling allocator_traits<A>::allocate() -
cptr，allocator_traits<A>::const_pointer类型的值，得到的转换，从ptr原文：cptr, a value of typeallocator_traits<A>::const_pointer, obtained by conversion fromptr -
vptr，allocator_traits<A>::void_pointer类型的值，得到的转换，从ptr原文：vptr, a value of typeallocator_traits<A>::void_pointer, obtained by conversion fromptr -
cvptr，值类型allocator_traits<A>::const_void_pointer，得到的转换cptr或vptr原文：cvptr, a value of typeallocator_traits<A>::const_void_pointer, obtained by conversion fromcptror fromvptr -
xptr的dereferencable的指针某种类型X原文：xptr, a dereferencable pointer to some typeX
| Expression | Requirements | Return type |
|---|---|---|
| A::pointer （可选的） | Satisfies NullablePointer and RandomAccessIterator
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| A::const_pointer （可选的） | A::pointer is convertible to A::const_pointer. Satisfies NullablePointer and RandomAccessIterator
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| A::void_pointer （可选的） | A::pointer is convertible to A::void_pointer
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| A::const_void_pointer （可选的） | A::pointer, A::const_pointer, and A::void_pointer are convertible to A::const_void_pointer
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| A::value_type | the type T
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| A::size_type （可选的） | A::size_type can represent the size of the largest object A can allocate
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unsigned integer type |
| A::difference_type （可选的） | A::difference_type can represent the difference of any two pointers to the objects allocated by A
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signed integer type |
| A::template rebind<U>::other （可选的[1]） | for any U, B::template rebind<T>::other is A
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the type B
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| *ptr | T&
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| *cptr | *cptr and *ptr identify the same object | const T&
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| ptr->m | same as (*ptr).m, if (*ptr).m is well-defined | the type of T::m
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| cptr->m | same as (*cptr).m, if (*cptr).m is well-defined | the type of T::m
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| static_cast<A::pointer>(vptr) | static_cast<A::pointer>(vptr) == ptr | A::pointer
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| static_cast<A::const_pointer>(cvptr) | static_cast<A::const_pointer>(vptr) == cptr | A::const_pointer
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| a.allocate(n) | allocates storage suitable for n objects of type T, but does not construct them. May throw exceptions.
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A::pointer
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| a.allocate(n, cptr) （可选的） | same as a.allocate(n), but may use cptr in unspecified manner to aid locality
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A::pointer
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| a.deallocate(ptr, n) | deallocates storage previously allocated by a call to a.allocate(n). Does not call destructors, if any objects were constructed, they must be destroyed before calling a.deallocate(). Does not throw exceptions. | (not used) |
| a.max_size() （可选的） | the largest value that can be passed to A::allocate()
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A::size_type
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| a1 == a2 | returns true only if the storage allocated by the allocator a1 can be deallocated through a2. Establishes reflexive, symmetric, and transitive relationship. Does not throw exceptions.
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bool |
| a1 != a2 | same as !(a1==a2) | bool |
| A a1(a) | Copy-constructs a1 such that a1 == a. Does not throw exceptions.
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| A a(b) | Constructs a such that B(a)==b and A(b)==a. Does not throw exceptions.
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| A a1(std::move(a)) | Constructs a1 such that it equals the prior value of a. Does not throw exceptions.
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| A a(std::move(b)) | Constructs a such that it equals the prior value of A(b). Does not throw exceptions.
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| a.construct(xptr, args) （可选的） | Constructs an object of type X in previously-allocated storage at the address pointed to by xptr, using args as the constructor arguments
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| a.destroy(xptr) （可选的） | Destructs an object of type X pointed to by xptr, but does not deallocate any storage.
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| a.select_on_container_copy_construction() （可选的） | Provides an instance of A to be used by the container that is copy-constructed from the one that uses a currently. Usually returns either a copy of a or a default-constructed A().
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A
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| a.propagate_on_container_copy_assignment （可选的） | true if the allocator of type A needs to be copied when the container that uses it is copy-assigned
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std::true_type or std::false_type or derived from such |
| a.propagate_on_container_move_assignment （可选的） | true if the allocator of type A needs to be copied when the container that uses it is move-assigned
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std::true_type or std::false_type or derived from such |
| a.propagate_on_container_swap （可选的） | true if the allocators of type A need to be swapped when two containers that use them are swapped
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std::true_type or std::false_type or derived from such |
注意事项：
[1]重新绑定是唯一可选的（提供由std :: allocator_traits），如果这分配器模板的形式SomeAllocator的，<T, Args>，args是零个或多个额外的模板参数.
原文：
[1] rebind is only optional (provided by std::allocator_traits) if this allocator is a template of the form SomeAllocator<T, Args>, where Args is zero or more additional template parameters.
