As a trivial example of a data structure with circular references, how about a doubly linked list? Admittedly there are alternative data structures to solve the same problem (eg an array), but that changes the performance characteristics too and may not be optimal for your particular use case.<p>This isn&#x27;t the point though. A general purpose programming language shouldn&#x27;t impose arbitrary restrictions on data structures like this. Even if such a restriction was in place it would have to be enforced at runtime which doesn&#x27;t sound like a trivial problem from a performance point of view.