CSharp: Visitor Pattern in donet core 3

 

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/// <summary> /// 访问者模式  Visitor Pattern /// geovindu,Geovin Du eidt    /// </summary> interface IEmployee {     /// <summary>     /// To set an employee name     /// </summary>     string Name { get; set; }     /// <summary>     /// To set an employee department     /// </summary>     string Dept { get; set; }     /// <summary>     /// To set an employee designation     /// </summary>     string Designation { get; set; }       /// <summary>     /// To display an employee details     /// </summary>     void DisplayDetails();         /// <summary>     ///Newly added for this example     ///To set years of Experience            ///</summary>     double Experience { get; set; }     /// <summary>     /// Newly added for this example     /// </summary>     /// <param name="visitor"></param>     void Accept(IVisitor visitor); } /// <summary> /// Leaf node /// </summary> class Employee : IEmployee {       /// <summary>     ///     /// </summary>     public string Name { get; set; }     /// <summary>     ///     /// </summary>     public string Dept { get; set; }     /// <summary>     ///     /// </summary>     public string Designation { get; set; }     /// <summary>     ///     /// </summary>     public double Experience { get; set; }     /// <summary>     /// Details of a leaf node     /// </summary>     public void DisplayDetails()     {         Console.WriteLine($"姓名：{Name} 工作在 {Dept} 部门.描述:{Designation}.经历 : {Experience} 年.");     }     /// <summary>     ///     /// </summary>     /// <param name="visitor"></param>     public void Accept(IVisitor visitor)     {         visitor.VisitEmployees(this);     }   } /// <summary> /// Non-leaf node /// </summary> class CompositeEmployee : IEmployee {       /// <summary>     ///     /// </summary>     public string Name { get; set; }       /// <summary>     ///     /// </summary>     public string Dept { get; set; }     /// <summary>     ///     /// </summary>     public string Designation { get; set; }     /// <summary>     ///     /// </summary>     public double Experience { get; set; }       //The container for child objects     //private List<IEmployee> subordinateList = new List<IEmployee>();     //Making it public now     /// <summary>     ///     /// </summary>     public List<IEmployee> subordinateList = new List<IEmployee>();       /// <summary>     /// To add an employee     /// </summary>     /// <param name="e"></param>     public void AddEmployee(IEmployee e)     {         subordinateList.Add(e);     }       /// <summary>     /// To remove an employee     /// </summary>     /// <param name="e"></param>     public void RemoveEmployee(IEmployee e)     {         subordinateList.Remove(e);     }       /// <summary>     /// Details of a composite node     /// </summary>     public void DisplayDetails()     {         Console.WriteLine($"\n姓名：{Name} 工作在 {Dept} 部门.描述:{Designation}.经历 : {Experience} 年.");         foreach (IEmployee e in subordinateList)         {             e.DisplayDetails();         }     }       public void Accept(IVisitor visitor)     {         visitor.VisitEmployees(this);     } } /// <summary> /// Visitor interface    /// </summary> interface IVisitor {     //To visit leaf nodes     void VisitEmployees(Employee employee);       //To visit composite nodes     void VisitEmployees(CompositeEmployee employee); } /// <summary> /// Concrete visitor class-PromotionCheckerVisitor /// </summary> class PromotionCheckerVisitor : IVisitor {      /// <summary>    ///    /// </summary>     string eligibleForPromotion = String.Empty;     /// <summary>     /// 工作经历大于15年     /// </summary>     /// <param name="employee"></param>     public void VisitEmployees(CompositeEmployee employee)     {         //We'll promote them if experience is greater than 15 years         eligibleForPromotion = employee.Experience > 15 ? "是" : "否";         Console.WriteLine($"{employee.Name} 来自于 {employee.Dept} 工作长于15年是否有资格升职? :{eligibleForPromotion}");       }     /// <summary>     /// 工作经历在于12年     /// </summary>     /// <param name="employee"></param>     public void VisitEmployees(Employee employee)     {         //We'll promote them if experience is greater than 12 years         eligibleForPromotion = employee.Experience > 12 ? "Yes" : "No";         Console.WriteLine($"{employee.Name} 来自于 {employee.Dept} 工作长于12年是否有资格升职? :{eligibleForPromotion}");     } }

　　

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using DictType = Dictionary<Type, Action<Expression, StringBuilder>>;    /// <summary>    /// 访问者模式  Visitor Pattern    /// geovindu,Geovin Du eidt       /// </summary>    public abstract class Expression    {    }    /// <summary>    ///    /// </summary>    public class DoubleExpression : Expression    {          /// <summary>        ///        /// </summary>        public double Value;        /// <summary>        ///        /// </summary>        /// <param name="value"></param>        public DoubleExpression(double value)        {            Value = value;        }    }    /// <summary>    ///    /// </summary>    public class AdditionExpression : Expression    {        /// <summary>        ///        /// </summary>        public Expression Left;        /// <summary>        ///        /// </summary>        public Expression Right;        /// <summary>        ///        /// </summary>        /// <param name="left"></param>        /// <param name="right"></param>        /// <exception cref="ArgumentNullException"></exception>        public AdditionExpression(Expression left, Expression right)        {            Left = left ?? throw new ArgumentNullException(paramName: nameof(left));            Right = right ?? throw new ArgumentNullException(paramName: nameof(right));        }    }      /// <summary>    ///    /// </summary>      public static class ExpressionPrinter    {        /// <summary>        ///        /// </summary>        private static DictType actions = new DictType        {            [typeof(DoubleExpression)] = (e, sb) =>            {                var de = (DoubleExpression)e;                sb.Append(de.Value);            },            [typeof(AdditionExpression)] = (e, sb) =>            {                var ae = (AdditionExpression)e;                sb.Append("(");                Print(ae.Left, sb);                sb.Append("+");                Print(ae.Right, sb);                sb.Append(")");            }        };        /// <summary>        ///        /// </summary>        /// <param name="e"></param>        /// <returns></returns>        public static string Print3(this Expression e)        {            var sb = new StringBuilder();            Print2(e, sb);            return sb.ToString();        }        /// <summary>        ///        /// </summary>        /// <param name="e"></param>        /// <param name="sb"></param>        private static void Print2(Expression e, StringBuilder sb)        {            actions[e.GetType()](e, sb);        }        /// <summary>        ///        /// </summary>        /// <param name="e"></param>        /// <param name="sb"></param>        private static void Print(Expression e, StringBuilder sb)        {            if (e is DoubleExpression de)            {                sb.Append(de.Value);            }            else            if (e is AdditionExpression ae)            {                sb.Append("(");                Print(ae.Left, sb);                sb.Append("+");                Print(ae.Right, sb);                sb.Append(")");            }            // breaks open-closed principle            // will work incorrectly on missing case        }    }

　　

调用：

 

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//访问者模式  Console.WriteLine("***访问者模式 Visitor Pattern with Composite Pattern Demo. ***");    #region Mathematics department  //2 lecturers work in Mathematics department  Employee mathTeacher1 = new Employee { Name = "老大", Dept = "应用数学", Designation = "讲师" ,Experience=13.7};  Employee mathTeacher2 = new Employee { Name = "老二", Dept = "应用数学", Designation = "讲师", Experience = 6.5 };    //The college has a Head of Department in Mathematics  CompositeEmployee hodMaths = new CompositeEmployee { Name = "老三", Dept = "数学", Designation = "数学系主任", Experience = 14 };    //Lecturers of Mathematics directly reports to HOD-Maths  hodMaths.AddEmployee(mathTeacher1);  hodMaths.AddEmployee(mathTeacher2);  #endregion    #region Computer Science department  //3 lecturers work in Computer Sc. department  Employee cseTeacher1 = new Employee { Name = "老四", Dept = "计算机科学", Designation = "讲师", Experience = 10.2 };  Employee cseTeacher2 = new Employee { Name = "老五", Dept = "计算机科学.", Designation = "讲师", Experience = 13.5 };  Employee cseTeacher3 = new Employee { Name = "老六", Dept = "计算机科学", Designation = "讲师", Experience = 7.3 };    //The college has a Head of Department in Computer science  CompositeEmployee hodCompSc = new CompositeEmployee { Name = "老幺", Dept = "计算机科学.", Designation = "计算机科学系主任.", Experience = 16.5 };    //Lecturers of Computer Sc. directly reports to HOD-CSE  hodCompSc.AddEmployee(cseTeacher1);  hodCompSc.AddEmployee(cseTeacher2);  hodCompSc.AddEmployee(cseTeacher3);  #endregion    #region Top level management  //The college also has a Principal  CompositeEmployee principal = new CompositeEmployee { Name = "族长", Dept = "规划监督管理部门", Designation = "校长", Experience = 21 };    //Head of Departments's of Maths and Computer Science directly reports to Principal.  principal.AddEmployee(hodMaths);  principal.AddEmployee(hodCompSc);  #endregion    /*   * Printing the leaf-nodes and branches in the same way.   * i.e. in each case, we are calling DisplayDetails() method.  */            Console.WriteLine("\nDetails of a college structure is as follows:");  //Prints the complete structure  principal.DisplayDetails();                   List<IEmployee> participants = new List<IEmployee>();    //For employees who directly reports to Principal  foreach (IEmployee e in principal.subordinateList)  {      // e.Accept(aVisitor);      participants.Add(e);  }  //For employees who directly reports to HOD-Maths  foreach (IEmployee e in hodMaths.subordinateList)  {      //e.Accept(aVisitor);      participants.Add(e);  }  //For employees who directly reports to HOD-Comp.Sc  foreach (IEmployee e in hodCompSc.subordinateList)  {      //e.Accept(aVisitor);      participants.Add(e);  }  Console.WriteLine("\n***访问者模式 Visitor starts visiting our composite structure***\n");  IVisitor visitor = new PromotionCheckerVisitor();  /* * Principal is already holding the highest position. * We are not checking whether he is eligible * for promotion or not. */  //principal.Accept(visitor);  //Visitor is traversing the participant list  foreach ( IEmployee  emp in participants)  {      emp.Accept(visitor);  }    //  var geovindu = new AdditionExpression( left: new DoubleExpression(1), right: new AdditionExpression( left: new DoubleExpression(2),  right: new DoubleExpression(3)));  var sb = new StringBuilder();  //ExpressionPrinter.Print2(e, sb);  Console.WriteLine(geovindu.Print3());

　　

 

输出：

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***访问者模式 Visitor Pattern with Composite Pattern Demo. ***   Details of a college structure is as follows:   姓名：族长 工作在 规划监督管理部门 部门.描述:校长.经历 : 21 年.   姓名：老三 工作在 数学 部门.描述:数学系主任.经历 : 14 年. 姓名：老大 工作在 应用数学 部门.描述:讲师.经历 : 13.7 年. 姓名：老二 工作在 应用数学 部门.描述:讲师.经历 : 6.5 年.   姓名：老幺 工作在 计算机科学. 部门.描述:计算机科学系主任..经历 : 16.5 年. 姓名：老四 工作在 计算机科学 部门.描述:讲师.经历 : 10.2 年. 姓名：老五 工作在 计算机科学. 部门.描述:讲师.经历 : 13.5 年. 姓名：老六 工作在 计算机科学 部门.描述:讲师.经历 : 7.3 年.   ***访问者模式 Visitor starts visiting our composite structure***   老三 来自于 数学 工作长于15年是否有资格升职? :否 老幺 来自于 计算机科学. 工作长于15年是否有资格升职? :是 老大 来自于 应用数学 工作长于12年是否有资格升职? :Yes 老二 来自于 应用数学 工作长于12年是否有资格升职? :No 老四 来自于 计算机科学 工作长于12年是否有资格升职? :No 老五 来自于 计算机科学. 工作长于12年是否有资格升职? :Yes 老六 来自于 计算机科学 工作长于12年是否有资格升职? :No (1+(2+3))