Weak References

Vala's memory management is based on automatic reference counting. Each time an object is assigned to a variable its internal reference count is increased by 1, each time a variable referencing an object goes out of scope its internal reference count is decreased by 1. If the reference count reaches 0 the object will be freed.

However, it is possible to form a reference cycle with your data structures. For example, with a tree data structure where a child node holds a reference to its parent and vice versa, or a doubly-linked list where each element holds a reference to its predecessor and the predecessor holds a reference to its successor.

In these cases objects could keep themselves alive simply by referencing to each other, even though they should be freed. To break such a reference cycle you can use the weak modifier for one of the references:

class Node {
    public weak Node prev;
    public Node next;
}

This topic is explained in detail on this page: Vala's Memory Management Explained.