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();     }   } }