Inheritance

Zap supports single class inheritance:

class Notification {
    prot recipient: String;

    fun init(recipient: String) {
        self.recipient = recipient;
    }

    pub fun send() String {
        return "Notification for " + self.recipient;
    }
}

class EmailNotification : Notification {
    fun init(recipient: String) {
        self.recipient = recipient;
    }

    pub fun send() String {
        return "Email sent to " + self.recipient;
    }
}

The subclass follows the colon after its name.

Protected members

prot allows the declaring class and its subclasses to access a member:

class NamedNotification : Notification {
    pub fun target() String {
        return self.recipient;
    }
}

Other callers cannot access recipient directly.

Base-class variables

A subclass instance may be stored in a base-class variable:

var notification: Notification =
    new EmailNotification("team@example.com");

Dynamic dispatch

Calling an overridden instance method through the base reference selects the subclass implementation:

println(notification.send());

Static methods do not use dynamic dispatch because they are called through the class rather than an object.

Use inheritance when callers genuinely need one polymorphic class interface. Prefer composition when one object merely uses another object to do part of its work.