Visitor design pattern
In the next design pattern, we are going to delegate some logic of an object's type to an external type called the visitor that will visit our object to perform operations on it.
Description
In the Visitor design pattern, we are trying to separate the logic needed to work with a specific object outside of the object itself. So we could have many different visitors that do some things to specific types.
For example, imagine that we have a log writer that writes to console. We could make the logger "visitable" so that you can prepend any text to each log. We could write a Visitor pattern that prepends the date, the time, and the hostname to a field stored in the object.
Objectives
With Behavioral design patterns we are mainly dealing with algorithms. Visitor patterns are not an exception. The objectives that we are trying to achieve are as follows:
To separate the algorithm of some type from its implementation within some other type
To improve the flexibility of some types...
