Is it possible for cyclic references to occur that prevent garbage collection in an automatic memory manager?

Yes, in iOS, when using Automatic Reference Counting (ARC), cyclic references (retain cycles) can occur. This happens when two or more objects hold strong references to each other, preventing their reference counts from reaching zero, and thus, they are not deallocated.

To prevent such situations, weak (weak) or unowned (unowned) references are used. For example, delegates are usually declared as weak to prevent cycles.

Example:

class Person {
    var apartment: Apartment?
}

class Apartment {
    weak var tenant: Person?  // weak reference prevents cycle
}

let john = Person()
let unit4A = Apartment()
john.apartment = unit4A
unit4A.tenant = john

In this example, tenant is a weak reference, so a cycle does not occur, and the objects will be properly deallocated by the garbage collector.