Question

I’m working on a .net app and I’m using an object that is composed of 5 Lists and 1 Hashtable. This object is used within a loop that iterates at least 500 times to run some analysis. On each loop this object should start empty, so I was wondering if it’s more efficient to call clear on all Lists and Hashtable or should I just re-initialize the object?

I know I could write code to benchmark this, but I’m wondering if someone has already been down this path?

Thanks.

Answer 1

While I agree with the other answer that this is a micro optimization, in the interests of answering the question, I have found that new List is slightly faster than Clear when using a List. Here’s my benchmark code:

static void Main(string[] args)
    {
        var start = DateTime.Now;
        List<string> lst = new List<string>();

        for (int i = 0; i < 3000; ++i)
        {
            //lst = new List<string>();
            lst.Clear();
            for (int j = 0; j < 500; ++j)
            {
                lst.Add(j.ToString());
            }
        }

        Console.WriteLine("{0} ms", ((DateTime.Now - start).Ticks / TimeSpan.TicksPerMillisecond));
        Console.ReadLine();
    }

Over five runs, new List averaged 340.8 ms, and Clear averaged 354.8 ms.

However, this results are so close that it’s clear that:

1. The difference is probably meaningless
2. I probably wasted my time by performing this benchmark