Visitor

// Visitor pattern -- Real World example

using System;
using System.Collections;

namespace DoFactory.GangOfFour.Visitor.RealWorld
{
  
  // MainApp startup application

  class MainApp
  {
    static void Main()
    {
      // Setup employee collection
      Employees e = new Employees();
      e.Attach(new Clerk());
      e.Attach(new Director());
      e.Attach(new President());

      // Employees are 'visited'
      e.Accept(new IncomeVisitor());
      e.Accept(new VacationVisitor());

      // Wait for user
      Console.Read();
    }
  }

  // "Visitor"

  interface IVisitor
  {
    void Visit(Element element);
  }

  // "ConcreteVisitor1"

  class IncomeVisitor : IVisitor
  {
    public void Visit(Element element)
    {
      Employee employee = element as Employee;

      // Provide 10% pay raise
      employee.Income *= 1.10;
      Console.WriteLine("{0} {1}'s new income: {2:C}",
        employee.GetType().Name, employee.Name,
        employee.Income);
    }
  }

  // "ConcreteVisitor2"

  class VacationVisitor : IVisitor
  {
    public void Visit(Element element)
    {
      Employee employee = element as Employee;
      
      // Provide 3 extra vacation days
      Console.WriteLine("{0} {1}'s new vacation days: {2}",
        employee.GetType().Name, employee.Name,
        employee.VacationDays);
    }
  }

  class Clerk : Employee
  {
    // Constructor
    public Clerk() : base("Hank", 25000.0, 14)
    {
    }
  }

  class Director : Employee
  {
    // Constructor
    public Director() : base("Elly", 35000.0, 16)
    {  
    }
  }

  class President : Employee
  {
    // Constructor
    public President() : base("Dick", 45000.0, 21)
    {  
    }
  }

  // "Element"

  abstract class Element
  {
    public abstract void Accept(IVisitor visitor);
  }

  // "ConcreteElement"

  class Employee : Element
  {
    string name;
    double income;
    int vacationDays;

    // Constructor
    public Employee(string name, double income,
      int vacationDays)
    {
      this.name = name;
      this.income = income;
      this.vacationDays = vacationDays;
    }

    // Properties
    public string Name
    {
      get{ return name; }
      set{ name = value; }
    }

    public double Income
    {
      get{ return income; }
      set{ income = value; }
    }

    public int VacationDays
    {
      get{ return vacationDays; }
      set{ vacationDays = value; }
    }

    public override void Accept(IVisitor visitor)
    {
      visitor.Visit(this);
    }
  }

  // "ObjectStructure"

  class Employees
  {
    private ArrayList employees = new ArrayList();

    public void Attach(Employee employee)
    {
      employees.Add(employee);
    }

    public void Detach(Employee employee)
    {
      employees.Remove(employee);
    }

    public void Accept(IVisitor visitor)
    {
      foreach (Employee e in employees)
      {
        e.Accept(visitor);
      }
      Console.WriteLine();
    }
  }
}