public class Person : IEquatable<Person>,IComparable<Person>
 {
  public int Id { get; private set; }
  public string FirstName { get; set; }
  public string LastName { get; set; }

  public override string ToString()
  {
   return String.Format("{0}, {1} {2}", Id, FirstName, LastName);
  } 

  public bool Equals(Person other)
  {
   if (other == null)
    return base.Equals(other);

   return this.FirstName == other.FirstName && this.LastName == other.LastName;
  }

  public int CompareTo(Person other)
  {
   if (other == null) throw new ArgumentNullException("other");

   int result = this.LastName.CompareTo(other.LastName);
   if (result == 0)
   {
    result = this.FirstName.CompareTo(other.FirstName);
   }

   return result;
  }

 }

 Person[] persons = {
    new Person { FirstName = "Simen03", LastName = "Go" },
    new Person { FirstName = "Simen02", LastName = "Go" },
    new Person { FirstName = "Simen01", LastName = "Go" }
   };
   Array.Sort(persons);
   foreach (var person in persons)
    Console.WriteLine(person);

// loop start (head: IL_009b)
   IL_008a: ldloc.2
   IL_008b: ldloc.3
   IL_008c: ldelem.ref
   IL_008d: stloc.s person
   IL_008f: ldloc.s person
   IL_0091: call void [mscorlib]System.Console::WriteLine(object)
   IL_0096: nop
   IL_0097: ldloc.3
   IL_0098: ldc.i4.1
   IL_0099: add
   IL_009a: stloc.3

   IL_009b: ldloc.3
   IL_009c: ldloc.2
   IL_009d: ldlen
   IL_009e: conv.i4
   IL_009f: blt.s IL_008a
  // end loop

 IEnumerator enumerator = persons.GetEnumerator();
   while (enumerator.MoveNext())
   {
    var person = enumerator.Current;
    Console.WriteLine(person);
   }

 static void Main(string[] args)
  {
   var helloCollection = new HelloCollection();
   foreach (string s in helloCollection)
   {
    Console.WriteLine(s);
   }
  }

  public class HelloCollection
  {
   public IEnumerator<string> GetEnumerator()
   {
    yield return "Hello";
    yield return "World";
   }
  }
  public class HelloCollectionOther
  {
   public IEnumerator GetEnumertor()
   {
    return new Enumerator(0);
   }
   public class Enumerator : IEnumerator<string>, IEnumerator, IDisposable
   {
    private int state;
    private string current;
    public Enumerator(int state)
    {
     this.state = state;
    }

    public string Current => throw new NotImplementedException();

    object IEnumerator.Current
    {
     get { return current; }
    }

    public void Dispose()
    {
     throw new NotImplementedException();
    }

    public bool MoveNext()
    {
     switch (state)
     {
      case 0:current = "hello";
       state = 1;
       return true;
      case 1:current = "world";
       state = 2;
       return true;
      case 2:
       break;
     }
     return false;
    }

    public void Reset()
    {
     throw new NotImplementedException();
    }
   }
  }