foreach + break vs linq FirstOrDefault performance difference

Question

I have two classes that perform date date range data fetching for particular days.

public class IterationLookup
{
    private IList          


        

Answer 1

Sometimes LINQ appears slower because the generation of delegates in a loop (especially a non-obvious loop over method calls) can add time. Instead, you may want to consider moving your finder out of the class to make it more generic (like your key selector is on construction):

public class LinqLookup
{
    private IList items = null;

    public IterationLookup(IEnumerable items, Func keySelector)
    {
        this.items = items.OrderByDescending(keySelector).ToList();
    }

    public TItem GetItem(Func selector)
    {
        return this.items.FirstOrDefault(selector);
    }
}

Since you don't use a lambda in your iterative code, this can be a bit of a difference since it has to create the delegate on each pass through the loop. Usually, this time is insignificant for every-day coding, and the time to invoke the delegate is no more expensive than other method calls, it's just the delegate creation in a tight loop that can add that little bit of extra time.

In this case, since the delegate never changes for the class, you can create it outside of the code you are looping through and it would be more efficient.

Update:

Actually, even without any optimization, compiling in release mode on my machine I do not see the 5x difference. I just performed 1,000,000 lookups on an Item that only has a DateTime field, with 5,000 items in the list. Of course, my data, etc, are different, but you can see the times are actually really close when you abstract out the delegate:

iterative : 14279 ms, 0.014279 ms/call

linq w opt : 17400 ms, 0.0174 ms/call

These time differences are very minor and worth the readability and maintainability improvements of using LINQ. I don't see the 5x difference though, which leads me to believe there's something we're not seeing in your test harness.