14

I tried to replace code 

foreach (var discovery in mpwrapper.parser.Discoveries)
{
   solution.AddFile("Discoveries", discovery.DisplayStringName + ".mpx", discovery);
}

with the following linq expression

mpwrapper.parser.Discoveries.Select(
                    s => solution.AddFile("Discoveries", s.DisplayStringName + ".mpx", s));

But got an error

The type arguments for method 'System.Linq.Enumerable.Select(System.Collections.Generic.IEnumerable, System.Func)' cannot be inferred from the usage. Try specifying the type arguments explicitly.

How to convert this foreach loop to linq query where I execute a method on each object in my IEnumerable collection?

Improve this question
3
  • I'm guessing that your solution.AddFile method doesn't return anything - would that be correct? Commented Jul 10, 2013 at 13:44
  • 1
    Select to execute code with side effects is improper use. Just do the foreach. Or List<T>.ForEach() which is a method that is expected to have side effects (= state changes outside the method). Commented Jul 10, 2013 at 13:47
  • 4
    As an aside, changing foreach loops to Linq just for the sake of it is one of the most common techniques to make code harder to understand and debug that I'm aware of in .NET. Commented Jul 10, 2013 at 13:47

7 Answers 7

Reset to default
20

I think what you need is the ForEach method ;)

mpwrapper.parser.Discoveries.ToList().ForEach(s => { solution.AddFile("Discoveries", s.DisplayStringName + ".mpx", s); });
Improve this answer
Sign up to request clarification or add additional context in comments.

5 Comments

Or just stick with foreach, which is clearer here IMO. See blogs.msdn.com/b/ericlippert/archive/2009/05/18/…. Note that without knowing the type of Discoveries, we don't know whether this will compile...
He's saying that it's an IEnumerable object, so it should compile. I answered what he asked regardless if it's better or not. But you're right, it might be better to use foreach instead.
No, there's no ForEach extension method on IEnumerable<T>. You could write one of course, but I'd advise against it.
I added the ToList() call that I had forgot ;P
will Linq foreach increase performance when compared to normal foreach on top of a list?
6

The problem is Select needs to return a value, but also Linq is not designed to mutate collections. Think of select as a transformation over the collection rather than a state change for each item

Maybe a foreach loop is the best solution here

Improve this answer

1 Comment

Well, LINQ works with mutable collections too - but isn't designed to mutate them itself.
4

LINQ stands for Language INtegrated Query... yet you aren't actually querying anything.

If mpwrapper.parser.Discoveries is a List<T>, you can use the ForEach method; or, if it is an IEnumerable, you could always add a ForEach extension method… but this is more a minor aesthetic change and has nothing to do with LINQ.

Improve this answer

Comments

2

I use a little cheat with the .All method. It simply requires a return boolean value and presents very neatly. I included a sample with embeded linq inside the .All

configurations.All(c =>
{
    var gcx = globalConfigurations.FirstOrDefault(gc =>
        gc.Type == c.Type && configurationGuids.Any(cGuid => gc.Guid == cGuid)
    );
    return true;
});
Improve this answer

Comments

1

Try this:

mpwrapper.parser.Discoveries.ToList()
    .ForEach(s =>
        solution.AddFile("Discoveries", s.DisplayStringName + ".mpx", s));
Improve this answer

Comments

1

The List<T>.ForEach method does the trick.

However, this method does not exist on IEnumerable<T>.

Improve this answer

Comments

0

If Discoveries is a list, then do it like this

mpwrapper.parser.Discoveries.ForEach(discovery => solution.AddFile("Discoveries", discovery .DisplayStringName + ".mpx", discovery);

If not, convert it to List first :)

Improve this answer

Comments

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service and acknowledge you have read our privacy policy.