Study HashSet and SortedList generics and remove generics in code of business logic

Note. This lesson is learned from Scott Allen C# Generic videos in Pluralsight.

1) Hashset (how to remove object duplicates)

HashSet type is supposed to identify duplicates and guarantee the uniqueness of stored objects, while the uniqueness/equality comparison shall be defined by the code.

HashSet has one construction that accepts a IEqualityComparer interface.

var departments = new SortedDictionary<string, HashSet<Employee>>();
Departments.Add("Sales", new HashSet<Employee>(new EmployeeComparer());
departments["Sales"].Add(new Employee{Name = "Joy" });
departments["Sales"].Add(new Employee{Name = "Joy" });
departments["Sales"].Add(new Employee{Name = "Joy" });

2) SortedSet (how to sort objects)

//SortedSet is similar, needs to implement IComparer<> interface
new SortedSet<Employee>(new EmployeeComparer());


public class EmployeeComparer : IEqualityComparer<Employee>, IComparer<Employee>
{
Equals ();
GetHashCode ();
}

3) Cleaner code - hide those fussy "new", "generic" keywords by create a new class to inherit

 
namespace Employees  
 {  
   public class Employee  
   {  
     public string Name { get; set; }  
   }  
   public class EmployeeComparer : IEqualityComparer<Employee>, IComparer<Employee>  
   {  
     public bool Equals(Employee x, Employee y)  
     {  
       return string.Equals(x.Name, y.Name);  
     }  
     public int GetHashCode(Employee obj)  
     {  
       return obj.Name.GetHashCode();  
     }  
     public int Compare(Employee x, Employee y)  
     {  
       return string.Compare(x.Name, y.Name);  
     }  
   }  
   public class DepartmentCollection : SortedDictionary<string, HashSet<Employee>>  
   {  
     public DepartmentCollection Add(string departmentName, Employee employee)  
     {  
       if (!ContainsKey(departmentName)) {   
         this.Add(departmentName, new HashSet<Employee>(new EmployeeComparer()));  
       }  
       this[departmentName].Add(employee);  
       return this;  
     }  
   }  
   class Program  
   {  
     static void Main(string[] args)  
     {  
       var departments = new DepartmentCollection();  
       departments.Add("Sales", new Employee { Name = "Xi" })  
             .Add("Sales", new Employee { Name = "Xi" })  
             .Add("Sales", new Employee { Name = "Liu" });  
       departments.Add("Engineers", new Employee { Name = "Jin" })  
             .Add("Engineers", new Employee { Name = "Jin" })  
             .Add("Engineers", new Employee { Name = "Jin" });  
       foreach (var item in departments)  
       {  
         Console.WriteLine(item.Key);  
         foreach (var employee in item.Value)  
         {  
           Console.WriteLine("\t" + employee.Name);  
         }  
       }  
       Console.ReadLine();  
     }  
   }  
 }