Last week, I stumbled upon the following piece of code:

IList<double> doubles = new List<double> {22.123, 400.12, 100.22};
foreach (int number in doubles)
{
    Console.WriteLine("The Current Number Is : {0}", number);
}

Can you see the bug in that code? We convert all of the doubles in the list to integers, truncating them. I was very surprised that the compiler didn’t warn me about this issue, especially because the compiler would not let me write this code:

Here we are talking about filtering list items again :). I got two comment suggesting the use of yield return.

James Curran said:

Don’t build a new list if you don’t have to.

private static IEnumerable EvenSlicker_FilterPositiveItems(IEnumerable t)

{

foreach(int n in t)

if (n > 0)

yield return n;

}

The advantage is if you try using the method this this:

foreach(int n in FilterPositiveItems(myList) {…}

Your way is O(2N) while mine is O(N)