Question

LINQ’s AsParallel returns ParallelQuery. I wonder if it’s possible to change this behavior so that I could compare the LINQ statement run with and without parallelism without actually changing the code? This behavior should be similar to Debug.Assert – when DEBUG preprocessor directive is not set, it’s optimized out. So I’d like to be able to make AsParallel return the same type without converting it to ParallelQuery.

I suppose I can declare my own extension method (because I can’t override AsParallel) and have that preprocessor directive analyzed within it:

    public static class MyExtensions
    {
#if TURN_OFF_LINQ_PARALLELISM
        public static IEnumerable<T> AsControllableParallel<T>(this IEnumerable<T> enumerable)
        {
            return enumerable;
        }
#else
        public static ParallelQuery<T> AsControllableParallel<T>(this IEnumerable<T> enumerable)
        {
            return enumerable.AsParallel();
        }
#endif
    }

I wonder if there is any other way. Am I asking for too much?

Answer 1

What about

            var result = 
                source
#if TURN_ON_LINQ_PARALLELISM
                .AsParallel()
#endif
                .Select(value => value.StartsWith("abcd"));