Is there a way, having one allocator object for type T, to use the SAME object to allocate memory for any other type. Maybe some magic with static_cast or rebind can help? Because right now I only have an idea of how to use rebind to derive the allocator type for the desired object type from the original allocator, but I don't understand how to use a ready-made allocator object to create any type of object.

CodePudding user response：

An allocator a of type A for value type T conforming to the standard requirements can be rebound to an allocator for type U via e.g.

std::allocator_traits<A>::rebind_alloc<U> b(a);

(although an allocator may support only a subset of all possible types U and fail to instantiate with others)

Then b can be used to allocate and deallocate objects of type U. You do not need to store this allocator b in addition to a however. Each time you perform this rebind from the same value of a it is guaranteed that the b objects compare equal, meaning that one can be used to deallocate memory allocated by the other.

Note that I didn't say that correctly in a previous comment: It is not guaranteed that an allocation allocated by a can be deallocated by b. So an allocator may be using e.g. different memory resources for different types, but the memory resources cannot be embedded into the allocator and copied on allocator copy or rebind.