Ability to reset IEnumerator generated using yield (C#)

Question

If I use yield instead of manually creating an IEnumerator, is it possible to implement IEnumerator.Reset?

Answer 1

My solution to this problem is to use a Wrapper class that can wrap any yielding function and reset:

public class Resettable : IEnumerator
{
  private IEnumerator inner;
  private Func func;

  public Resettable(Func func)
  {
    this.func = func;
    inner = func.Invoke();
  }

  public bool MoveNext()
  {
    return inner.MoveNext();
  }

  public object Current { get { return inner.Current; } }

  public void Reset()
  {
    inner = func.Invoke();
  }

  public static Resettable Make(Func func)
  {
    return new Resettable(func);
  }

  public static Resettable Make(Func func, T1 a1)
  {
    Func capture = () => { return func.Invoke(a1); };
    return new Resettable(capture);
  }

  public static Resettable Make(Func func, T1 a1, T2 a2)
  {
    Func capture = () => { return func.Invoke(a1, a2); };
    return new Resettable(capture);
  }

  public static Resettable Make(Func func, T1 a1, T2 a2, T3 a3)
  {
    Func capture = () => { return func.Invoke(a1, a2, a3); };
    return new Resettable(capture);
  }

  // add more of these to support more arguments
}

then, instead of calling your yielding method directly, you call Resettable.Make(YourMethod, ..arguments..);

so, here's an example usage:

public class Program
{ 
  static IEnumerator YieldTest(int start)
  {
    yield return start;
    yield return start + 1;
    yield return start + 2;
  }
    
  public static void Main()
  {
    // IEnumerator en = YieldTest(5);
    IEnumerator en = Resettable.Make(YieldTest, 5);

    while(en.MoveNext())
    {
      Console.WriteLine("value: "+en.Current.ToString());
    }
    Console.WriteLine("Reset");
    en.Reset();
    while(en.MoveNext())
    {
      Console.WriteLine("value: "+en.Current.ToString());
    }
  }
}

Output:

value: 5
value: 6
value: 7
Reset
value: 5
value: 6
value: 7