Enumerating over Select’s index
My mind was wandering, as usual when it is not 100% occupied, and I remembered that the Select LINQ function has an overload that gives you the index into the enumeration and it uses an int. So, I thought what’s going to happen if I have longer enumeration and it goes over the range of the int?
Most of the time it’s probably fine because most of the collections and arrays and … are limited by having Count/Length as an int. But obviously you can create an enumeration that’s using the yield return keywords and basically keep iterating over the range of an int. So, I did that and this is the result.
static class Program
{
static void Main()
{
foreach (var i in ALotOfStrings().Select((s, i) => i))
{ }
}
static IEnumerable<string> ALotOfStrings()
{
for (var j = 0L; j < long.MaxValue; j++)
{
yield return string.Empty;
}
}
}
Running this gives an uninspiring exception System.OverflowException: Arithmetic operation resulted in an overflow.. On the other it makes sense what else should happen (except for rolling over), right?
Hmm, how is it actually implemented? Is there some magic or is it a simple iteration that increments a counter? Well, let’s see.
private static IEnumerable<TResult> SelectIterator<TSource, TResult>(IEnumerable<TSource> source, Func<TSource, int, TResult> selector)
{
int index = -1;
foreach (TSource element in source)
{
checked
{
index++;
}
yield return selector(element, index);
}
}
Oh my, all this exploration is getting more and more boring. Time to get back to work.
