If `Allocator::select_on_container_copy_construction` exists and has the right signature, the allocator will be constructed from its result.
If若 `Allocator::select_on_container_copy_construction` exists and has the right signature, the allocator will be constructed from its result.存在且具有正确的签名,则将根据其结果来构造分配器。
If若 `Allocator::select_on_container_copy_construction`exists and has the right signature, the allocator will be constructed from its result.存在且具有正确的签名,则将根据其结果来构造分配器。