DESIGN-PATTERNS Course

Visitor

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A visitor can do methods defined in an interface. Then you will have concrete classes taking a visitor and executing (or not) some code.

From what I understood

  • create an abstract class with an accept method, taking a visitor
  • a visitor is an interface of the methods that may be implemented according to the kind of visitor
  • then you create visitors
  • and you create concrete classes inheriting the abstract class that may do something different according to the visitor

I have seen it used in parsers, like in JetBrains's R language parser.

There are examples and explanations here.