Define an Extension Method for IEnumerable<T> which returns IList<T>

Hi experts

Im trying to better understand linq and I was trying to have an Extension Method that returns a IList<T> instead of IEnumerable<T>

I have an Extension Method for IEnumerable<T> which returns IEnumerable<T>

static IEnumerable<T> Where<T>(this IEnumerable<T> data, Func<T, bool> predicate)
{
    foreach(T value in data)
    {
        if(predicate(value)) yield return value;
    }
}

Open in new window


if I use this, I will get this error of "ïs not an iterator interface"

static IList<T> Where<T>(this IEnumerable<T> data, Func<T, bool> predicate)
        {
            //Error	1	The body of 'ConsoleApplication1.EnumerableExtensions.Where<T>
            //(System.Collections.Generic.IEnumerable<T>, System.Func<T,bool>)' 
            //cannot be an iterator block because 'System.Collections.Generic.IList<T>' 
            //is not an iterator interface 

            foreach (T value in data)
            {
                if (predicate(value)) yield return value;
            }
        }

Open in new window


I think that the way to do it is like this

static IList<T> Where<T>(this IEnumerable<T> data, Func<T, bool> predicate)
        {
            return Enumerable.Where(data, predicate).ToList();
        }

Open in new window


Is it valid for all cases? I will like to undertand it better

Thanks
JoseHidalgoAsked:
Who is Participating?
I wear a lot of hats...

"The solutions and answers provided on Experts Exchange have been extremely helpful to me over the last few years. I wear a lot of hats - Developer, Database Administrator, Help Desk, etc., so I know a lot of things but not a lot about one thing. Experts Exchange gives me answers from people who do know a lot about one thing, in a easy to use platform." -Todd S.

wdosanjosCommented:
You get that error because you are using the yield return construct, which mandates the method to return either IEnumerable or IEnumerable<T>.
0

Experts Exchange Solution brought to you by

Your issues matter to us.

Facing a tech roadblock? Get the help and guidance you need from experienced professionals who care. Ask your question anytime, anywhere, with no hassle.

Start your 7-day free trial
Bob LearnedCommented:
I don't understand, as LINQ already provides the ToList extension method for IEnumerable.
0
It's more than this solution.Get answers and train to solve all your tech problems - anytime, anywhere.Try it for free Edge Out The Competitionfor your dream job with proven skills and certifications.Get started today Stand Outas the employee with proven skills.Start learning today for free Move Your Career Forwardwith certification training in the latest technologies.Start your trial today
C#

From novice to tech pro — start learning today.

Question has a verified solution.

Are you are experiencing a similar issue? Get a personalized answer when you ask a related question.

Have a better answer? Share it in a comment.