Should be fine (see below). Was there a specific issue you were
seeing?

Marc

using System;
using System.Collections;
using System.Collections.Generic;

struct MyTuple : IEnumerable<int>
{
   public readonly int a, b, c, d, e; // lazy... should be props
   public MyTuple(int a, int b, int c, int d, int e)
   {
       this.a = a; this.b = b; this.c = c;
       this.d = d; this.e = e;
   }
   public IEnumerator<int> GetEnumerator()
   {
       yield return a;
       yield return b;
       yield return c;
       yield return d;
       yield return e;
   }
   IEnumerator IEnumerable.GetEnumerator()
   {
       return GetEnumerator();
   }
}
static class Program
{
   static void Main()
   {
       MyTuple tuple = new MyTuple(1, 2, 3, 4, 5);
       foreach(int x in tuple) {
           Console.WriteLine(x);
       }
   }
}

public struct StructTest : IEnumerator
{
#region IEnumerator Members
public object Current
{
get { throw new Exception("The method or operation is not implemented."); }
}
public bool MoveNext()
{
throw new Exception("The method or operation is not implemented.");
}
public void Reset()
{
throw new Exception("The method or operation is not implemented.");
}
#endregion
}

For a class it is the same but then public class instead of public struct

Ah, sorry, I misread IEnumerator as IEnumerable.

Yes it is perfectly possible, but be careful; this type of usage often
means making the struct mutable (otherwise what would MoveNext do...)
- which can cause problems if used in certain ways... but the core MS
libs use struct enumerators in a number of places -
List<T>.Enumerator, for example.

Personally I wouldn't recommend writing your own enumerator; in C# 2
and above the yield syntax does it for you...

Marc