如果标准容器元素类型和std :: allocator类型不同，那么它是错误的吗？ [英] Is it wrong if the standard container element type and std::allocator type are different?

问题描述

从这里（很旧）：

同样重要的是，用于分配器模板
参数的类型和用作标准
容器中的元素类型的类型是一致的。例如：

It's also important that the type used for the allocator template parameter and the type used as the element type in a standard container agree. For instance:

std::list<int, std::allocator<long> >                    // Wrong!

无效。

问题

上述语句是否正确（或是否正确）？我做的任何测试似乎工作正常，无论我在 T 在 std :: allocator 中。例如， std :: vector< int，std :: allocator< std :: string>> 编译和工作精细推回和擦除元素等
（从我理解 std :: allocator< std :: string> :: rebind< int> :: other 是使这个工作的魔法）。

Is the above statement correct (or was it ever correct)? Any tests I have done seem to work fine no matter what I put for T in std::allocator. For example, std::vector<int, std::allocator<std::string>> compiled and worked fine pushing back and erasing elements, etc. (From what I understand std::allocator<std::string>::rebind<int>::other is the magic that makes this work).

推荐答案

编辑：在[containers.requirements.general]中，Allocator感知容器需求指示 allocator_type： ：value_type 与 Container :: value_type 相同。

In [containers.requirements.general], the Allocator-aware container requirements indicate that the allocator_type::value_type is the same as Container::value_type.

传递具有不同 value_type 的分配器类型，尽管至少一个实现仅使用 allocator_traits< ...> :: rebind< value_type> 以获取正确的分配器。

So it's ill formed to pass in an allocator type with a different value_type, although at least one implementation simply uses allocator_traits<...>::rebind<value_type> to get the correct allocator.

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