Question

Within the following query i would like to add:

• Trace.WriteLine(i.Name)

• and get a count of tasks without an additional enumeration afterwards (without a separate int count = tasks.Count())

Sample Query

        var tasks = (
            from i in items
            where i.IsValid
            orderby i.Priority 
            select i.GetTask())
            .Take(100);

         await TaskEx.WhenAll(tasks);

I know how to achieve that with subsequent/extra enumerations, but I was wondering how to do all that in one enumeration? It’s important because the i.IsValid operation is actually expensive and I would like to only call that once in order to do the filtering…

Answer 1

Given that you’re only taking 100 items anyway, I’d just use ToList to force it to be in a list:

var tasks = (from i in items
             where i.IsValid
             orderby i.Priority 
             select i.GetTask()).Take(100).ToList();

Then you can iterate over them to trace them, easily get the count, and pass the list to TaskEx.WhenAll.