C# — Yield

Yield is present in C# since 2.0, using a yield return construct similar to yield in Python.

public object Solve()
{
  return Fibonnaci().Where(i => i % 2 == 0).Sum();
}
private static IEnumerable<int> Fibonnaci()
{
  int t1 = 1,
  t2 = 2;
  yield return t1;
  yield return t2;

  while (t2 < 4000000)
  {
    var aux = t2;
    t2 += t1;
    t1 = aux;
    yield return t2;
  }
}

With a yield return, the function automatically keeps its state during the iteration.