How to remove elements from a generic list while iterating over it?

Question

I am looking for a better pattern for working with a list of elements which each need processed and then depending on the outcome are removed from

Answer 1

For loops are a bad construct for this.

Using while

var numbers = new List(Enumerable.Range(1, 3));

while (numbers.Count > 0)
{
    numbers.RemoveAt(0);
}

But, if you absolutely must use for

var numbers = new List(Enumerable.Range(1, 3));

for (; numbers.Count > 0;)
{
    numbers.RemoveAt(0);
}

Or, this:

public static class Extensions
{

    public static IList Remove(
        this IList numbers,
        Func predicate)
    {
        numbers.ForEachBackwards(predicate, (n, index) => numbers.RemoveAt(index));
        return numbers;
    }

    public static void ForEachBackwards(
        this IList numbers,
        Func predicate,
        Action action)
    {
        for (var i = numbers.Count - 1; i >= 0; i--)
        {
            if (predicate(numbers[i]))
            {
                action(numbers[i], i);
            }
        }
    }
}

Usage:

var numbers = new List(Enumerable.Range(1, 10)).Remove((n) => n > 5);