Visitor Pattern

An OOP Design Pattern that separates algorithm from object structure. A visitor is an object with methods for acting on various kinds of other objects.

• Allows adding more functionality to a class without modifying its structure, thereby allowing inheriting classes to remain the same

Example

class BinaryOperation : public Expression {
	// call a visitor method named visit that takes this current binary operator as the argument
	v.visit(*this);
}

class PrintingVisitor : public Visitor {
	void visit(BinaryOperator &o){
		std::cout << '('; // print opening parenthesis
		o.left.accept(*this); // print left operand
		std::cout << o.op; // print operator
		o.right.accept(*this); // print right operand
		std::cout << ')'; // print closing parenthesis
	}
}