Is it possible to implement a mechanism that tracks objects using weak references without preventing their garbage collection?

Yes, in iOS (and in Swift) there is a mechanism of weak references, which allows tracking objects without retaining them in memory and preventing their deletion by the garbage collector (ARC).

A weak reference does not increase the reference count of an object, so when there are no strong references to the object, it is deallocated from memory.

Example of using a weak reference in Swift:

class Person {
    let name: String
    init(name: String) {
        self.name = name
    }
}

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

var person: Person? = Person(name: "Ivan")
var apartment: Apartment? = Apartment()
apartment?.tenant = person

person = nil  // the Person object will be removed, as there are no strong references

print(apartment?.tenant)  // nil

Thus, weak references allow tracking objects without preventing their deletion.