Inheritance and abstract templates

List parent templates after :. A child inherits fields and methods. Use override to replace an inherited implementation.

abstract data Readable {
    abstract func read(): int
}

data Counter: Readable {
    var value: int = 5

    override func read(): int {
        return this.value
    }
}

func main() {
    var counter = Counter()
    print(counter.read())
}

abstract data defines a shared interface for children. abstract func declares a method signature. A concrete child supplies all inherited abstract methods before you create its instances.

Separate multiple parents with commas, such as data Combined: First, Second. Resolve shared member names through explicit implementations and compatible field types.