ARC and Weak Refs

ARC

Class instances are heap allocated with new and managed with ARC.

global var destroyed: Int = 0;

class Buffer {
    fun deinit() {
        destroyed = destroyed + 1;
    }
}

Deterministic cleanup

When the last strong reference disappears, deinit() can run immediately.

Weak references

Use weak to avoid reference cycles:

class Parent {}

class Child {
    priv parent: weak Parent;

    pub fun setParent(parent: weak Parent) {
        self.parent = parent;
    }
}

Checking liveness

Zap also supports:

• alive(weakRef)
• lock(weakRef)

Example

class Parent {
    pub fun current() Int {
        return 7;
    }
}

class Child {
    priv parent: weak Parent;

    pub fun setParent(parent: weak Parent) {
        self.parent = parent;
    }

    pub fun readParent() Int {
        if !alive(self.parent) {
            return -1;
        }
        var parent: Parent = lock(self.parent);
        return parent.current();
    }
}