Ballerina Object Visitor Pattern

visitor_pattern.bal

import ballerina/io;

public type Element object {
    public function accept(Visitor visitor);
};

public class ConcreteElementA {
    *Element;

    public function accept(Visitor visitor) {
        visitor.visitConcreteElementA(self);
    }

    public function operationA() returns string {
        return "ConcreteElementA operation";
    }
};

public class ConcreteElementB {
    *Element;

    public function accept(Visitor visitor) {
        visitor.visitConcreteElementB(self);
    }

    public function operationB() returns string {
        return "ConcreteElementB operation";
    }
};


public type Visitor object {
    public function visitConcreteElementA(ConcreteElementA element);
    public function visitConcreteElementB(ConcreteElementB element);
};


public class ConcreteVisitor1 {
    *Visitor;

    public function visitConcreteElementA(ConcreteElementA element) {
        io:println("ConcreteVisitor1: ", element.operationA());
    }

    public function visitConcreteElementB(ConcreteElementB element) {
        io:println("ConcreteVisitor1: ", element.operationB());
    }
};

public function main() {
    Element[] elements = [new ConcreteElementA(), new ConcreteElementB()];
    Visitor visitor1 = new ConcreteVisitor1();

    clientCode(elements, visitor1);
}

function clientCode(Element[] elements, Visitor visitor) {
    foreach var element in elements {
        element.accept(visitor);
    }
}