A more practical demonstration of a base class constraint : Base class constaint : Generic C# Examples

    
using  System;  
  
class  NotFoundException  :  ApplicationException  {}  
  
class  UserID  {  
    string  name;  
    string  number;  
  
    public  UserID(string  n,  string  num)  {  
        name  =  n;  
        number  =  num;  
    }  
  
    public  string  Number  {  
        get  {  return  number;  }  
        set  {  number  =  value;  }  
    }  
  
    public  string  Name  {  
        get  {  return  name;  }  
        set  {  name  =  value;  }  
    }  
}  
  
class  Employee  :  UserID  {  
    public  Employee(string  n,  string  num)  :  base(n,  num)  
    {  

    }  
}  
  
class  Manager  :  UserID  {  
    public  Manager(string  n,  string  num)  :  
        base(n,  num)  {  }  
}  
  
class  Guest  {  
}  
  
class  IDList<T>  where  T  :  UserID  {  
    T[]  userIDList;  
    int  end;  
  
    public  IDList()  {    
        userIDList  =  new  T[10];  
        end  =  0;  
    }  
  
    public  bool  add(T  newEntry)  {  
        if(end  ==  10)  return  false;  
  
        userIDList[end]  =  newEntry;  
        end++;  
  
        return  true;  
    }  
  
    public  T  findByName(string  name)  {  
        for(int  i=0;  i<end;  i++)  {  
            if(userIDList[i].Name  ==  name)    
                return  userIDList[i];  
  
        }  
        throw  new  NotFoundException();  
    }  
  
    public  T  findByNumber(string  number)  {  
  
        for(int  i=0;  i<end;  i++)  {  
            if(userIDList[i].Number  ==  number)    
                return  userIDList[i];  
        }  
        throw  new  NotFoundException();  
    }  
}  
  
class  MainClass  {  
    public  static  void  Main()  {  
        IDList<Employee>  plist  =  new  IDList<Employee>();  
        plist.add(new  Employee("T",  "1"));  
        plist.add(new  Employee("G",  "6"));  
        plist.add(new  Employee("M",  "5"));  
  
        try  {  
            Employee  frnd  =  plist.findByName("T");  
            Console.Write(frnd.Name  +  ":  "  +  frnd.Number);  
        }  catch(NotFoundException)  {  
            Console.WriteLine("Not  Found");  
        }  
  
        Console.WriteLine();  
  
        IDList<Manager>  plist2  =  new  IDList<Manager>();  
        plist2.add(new  Manager("G",  "8"));  
        plist2.add(new  Manager("C",  "9"));  
        plist2.add(new  Manager("N",  "2"));  
  
        try  {  
            Manager  sp  =  plist2.findByNumber("8");  
            Console.WriteLine(sp.Name  +  ":  "  +  sp.Number);  
        }  catch(NotFoundException)  {  
                Console.WriteLine("Not  Found");  
        }  
    }  
}