Interface constraints in generics, C#

Interface constraints in generics

//Title of this code
//Rextester.Program.Main is the entry point for your code. Don't change it.
//Compiler version 4.0.30319.17929 for Microsoft (R) .NET Framework 4.5

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text.RegularExpressions;

namespace Rextester
{
    public NotFoundException() : base() { }

public NotFoundException(string message) : base(message) { }

public NotFoundException(string message, Exception innerException) :

base(message, innerException) { }

protected NotFoundException(

System.Runtime.Serialization.SerializationInfo info,

System.Runtime.Serialization.StreamingContext context) :

base(info, context) { }

// An interface that supports a name and phone number.

public interface IPhoneNumber {

string Number {

get;

set;

}

string Name {

get;

set;

}

// A class of phone numbers for friends.

// It implements IPhoneNumber.

class Friend : IPhoneNumber {

public Friend(string n, string num, bool wk) {

Name = n;

Number = num;

IsWorkNumber = wk;

}

public bool IsWorkNumber { get; private set; }

// Implement IPhoneNumber.

public string Number { get; set; }

public string Name { get; set; }

// ...

// A class of phone numbers for suppliers.

class Supplier : IPhoneNumber {

public Supplier(string n, string num) {

Name = n;

Number = num;

}
    public string Number { get; set; }

public string Name { get; set; }

// ...

// Notice that this class does not implement IPhoneNumber.

class EmailFriend {

// ...

// PhoneList can manage any type of phone list

// as long as it implements IPhoneNumber.

class PhoneList<T> where T : IPhoneNumber {

T[] phList;

int end;

public PhoneList() {

phList = new T[10];

end = 0;

}

public bool Add(T newEntry) {

if(end == 10) return false;

phList[end] = newEntry;

end++;

return true;

}

// Given a name, find and return the phone info.

public T FindByName(string name) {

for(int i=0; i<end; i++) {

// Name can be used because it is a member of

// IPhoneNumber, which is the interface constraint.

if(phList[i].Name == name)

return phList[i];

}

// Name not in list.

throw new NotFoundException();

}

// Given a number, find and return the phone info.

public T FindByNumber(string number) {
     for(int i=0; i<end; i++) {

// Number can be used because it is also a member of

// IPhoneNumber, which is the interface constraint.

if(phList[i].Number == number)

return phList[i];

}
     // Number not in list.

throw new NotFoundException();

// ...
 }
    
    public class Program
    {
        public static void Main(string[] args)
        {
            //Your code goes here
            // The following code is OK because Friend

// implements IPhoneNumber.

PhoneList<Friend> plist = new PhoneList<Friend>();

plist.Add(new Friend("Tom", "555-1234", true));

plist.Add(new Friend("Gary", "555-6756", true));

plist.Add(new Friend("Matt", "555-9254", false));

try {

// Find the number of a friend given a name.

Friend frnd = plist.FindByName("Gary");

Console.Write(frnd.Name + ": " + frnd.Number);

if(frnd.IsWorkNumber)

Console.WriteLine(" (work)");

else

Console.WriteLine();

} catch(NotFoundException) {

Console.WriteLine("Not Found");

}

Console.WriteLine();

// The following code is also OK because Supplier

// implements IPhoneNumber.

PhoneList<Supplier> plist2 = new PhoneList<Supplier>();

plist2.Add(new Supplier("Global Hardware", "555-8834"));

plist2.Add(new Supplier("Computer Warehouse", "555-9256"));

plist2.Add(new Supplier("NetworkCity", "555-2564"));
            try {

// Find the name of a supplier given a number.

Supplier sp = plist2.FindByNumber("555-2564");

Console.WriteLine(sp.Name + ": " + sp.Number);

} catch(NotFoundException) {

Console.WriteLine("Not Found");

}

// The following declaration is invalid because EmailFriend

// does NOT implement IPhoneNumber.

// PhoneList<EmailFriend> plist3 =

// new PhoneList<EmailFriend>(); // Error!
        }
    }
}


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