I have a data structure which has an add function. When the user instantiates a new data structure object, she can specify an algorithm which will be executed each time the add function is called and alters the newly inserted value based on the previous values in the data structure. The algorithm needs to have access to all the data in the data structure.

Thus the data structure needs to store an algorithm object (since this is called each time the add is executed). On the other hand the algorithm needs access the data structure, and thus needs to store the data structure object.

I think situations where class A has an instance of class B and class B has an instance of class A are usually undesirable.

Does anybody have an idea how to solve this recurrence here?