What does the Visitor pattern do?

The purpose of a Visitor pattern is to define a new operation without introducing the modifications to an existing object structure. Simply put, we’ll have to do is to add a function which accepts the visitor class to each element of the structure.

Why the Visitor pattern is bad?

The visitor pattern is one of the most overrated and yet underestimated patterns in object-oriented design. Overrated, because it is often chosen too quickly (possibly by an architecture astronaut), and then bloats an otherwise very simple design, when added in the wrong way.

What is Visitor pattern in C++?

Visitor is a behavioral design pattern that allows adding new behaviors to existing class hierarchy without altering any existing code. Read why Visitors can’t be simply replaced with method overloading in our article Visitor and Double Dispatch.

What is the difference between visitor and composite design patterns?

Composite Pattern is a structural pattern that helps one create tree-like hierarchial structures whereas the Visitor Pattern is a behavioral pattern that allows a visitor object to “visit” each element in a structural hierarchy to perform some operation/behavior on that element.

How does visitor work in visitor design pattern?

In the Visitor Design Pattern, we use a Visitor object which changes the executing algorithm of an element object. In this way, when the visitor varies, the execution algorithm of the element object can also vary.

What is the visitor pattern in UML sequence?

The UML sequence diagram shows the run-time interactions: The Client object traverses the elements of an object structure ( ElementA,ElementB) and calls accept (visitor) on each element. First, the Client calls accept (visitor) on ElementA, which calls visitElementA (this) on the accepted visitor object.

When to call the accept method in the visitor pattern?

When an operation is to be performed which is implemented using the Visitor pattern, it calls the accept method of the top-level element(s). When the accept method is called in the program, its implementation is chosen based on both the dynamic type of the element and the static type of the visitor.

How is a visitor dispatched to an element?

Clients traverse the object structure and call a dispatching operation accept (visitor) on an element — that “dispatches” (delegates) the request to the “accepted visitor object”. The visitor object then performs the operation on the element (“visits the element”).