add full implementin last Patern ✌️

Author: VanHakobyan

Visitor/Readme.md

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 <p align="center"><img src="https://www.codeproject.com/KB/architecture/Visitor_Design_Pattern/visitorS.JPG"></p>
+
+### Problem
+
+Many distinct and unrelated operations need to be performed on node objects in a heterogeneous aggregate structure. You want to avoid "polluting" the node classes with these operations. And, you don't want to have to query the type of each node and cast the pointer to the correct type before performing the desired operation.
+
+### Discussion
+
+Visitor's primary purpose is to abstract functionality that can be applied to an aggregate hierarchy of "element" objects. The approach encourages designing lightweight Element classes - because processing functionality is removed from their list of responsibilities. New functionality can easily be added to the original inheritance hierarchy by creating a new Visitor subclass.
+
+Visitor implements "double dispatch". OO messages routinely manifest "single dispatch" - the operation that is executed depends on: the name of the request, and the type of the receiver. In "double dispatch", the operation executed depends on: the name of the request, and the type of TWO receivers (the type of the Visitor and the type of the element it visits).
+
+The implementation proceeds as follows. Create a Visitor class hierarchy that defines a pure virtual visit() method in the abstract base class for each concrete derived class in the aggregate node hierarchy. Each visit() method accepts a single argument - a pointer or reference to an original Element derived class.
+
+Each operation to be supported is modelled with a concrete derived class of the Visitor hierarchy. The visit() methods declared in the Visitor base class are now defined in each derived subclass by allocating the "type query and cast" code in the original implementation to the appropriate overloaded visit() method.
+
+Add a single pure virtual accept() method to the base class of the Element hierarchy. accept() is defined to receive a single argument - a pointer or reference to the abstract base class of the Visitor hierarchy.
+
+Each concrete derived class of the Element hierarchy implements the accept() method by simply calling the visit() method on the concrete derived instance of the Visitor hierarchy that it was passed, passing its "this" pointer as the sole argument.
+
+Everything for "elements" and "visitors" is now set-up. When the client needs an operation to be performed, (s)he creates an instance of the Visitor object, calls the  accept() method on each Element object, and passes the Visitor object.
+
+The accept() method causes flow of control to find the correct Element subclass. Then when the visit() method is invoked, flow of control is vectored to the correct Visitor subclass. accept() dispatch plus visit() dispatch equals double dispatch.
+
+The Visitor pattern makes adding new operations (or utilities) easy - simply add a new Visitor derived class. But, if the subclasses in the aggregate node hierarchy are not stable, keeping the Visitor subclasses in sync requires a prohibitive amount of effort.
+
+An acknowledged objection to the Visitor pattern is that is represents a regression to functional decomposition - separate the algorithms from the data structures. While this is a legitimate interpretation, perhaps a better perspective/rationale is the goal of promoting non-traditional behavior to full object status.
+
+### Example
+
+The Visitor pattern represents an operation to be performed on the elements of an object structure without changing the classes on which it operates. This pattern can be observed in the operation of a taxi company. When a person calls a taxi company (accepting a visitor), the company dispatches a cab to the customer. Upon entering the taxi the customer, or Visitor, is no longer in control of his or her own transportation, the taxi (driver) is.
+
+<img src="https://sourcemaking.com/files/v2/content/patterns/Visitor_example1.svg">
+
+* Source code <a href="https://github.com/VanHakobyan/DesignPatterns/tree/master/Visitor/Visitor">her</p>