C # LINQ - does filter pick null when used with a method group?
Today I wrote some code that takes a list of instances of class A and creates a list of instances of class B using a static factory method:
public abstract class B
{
public static B CreateB(A a)
{
// return a new B instance or null if a B instance can't be created
}
}
I needed to filter out zeros, so I used LINQ to do both:
var bList = aList.Select(a => B.CreateB(a)).Where(b => b != null).ToList();
The code works as expected, but I noticed that Resharper was suggesting, when calling CreateB, I must "convert to method group". I wondered what this means and found some interesting answers on this site. For example: What is a method group in C #? and Asad's comment on the verse answer here Filtering null values in Select (.Select (x => transform (x)) maybe. Select (transform))
So, I changed my code to:
var bList = aList.Select(B.CreateB).Where(b => b != null).ToList();
This works as expected too, but now I'll get to my question. Resharper now tells me where the lambda expression can be removed because b! = Null is "always true".
I've played around and Resharper is correct, but why? Why is there a difference in the returned Select () collection when I use a method group? Why does the Select () function seem to filter out zeros from the collection when I use a group of methods?
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Both aList.Select(a => B.CreateB(a)).Where(b => b != null).ToList();
both aList.Select(B.CreateB).Where(b => b != null).ToList();
use the same method overload Select
.
I tested it using LinqPad and got the following output:
So, it Select
doesn't filter anything. Which version of Resharper and VisualStudio are you using?
Latest ReSharper on VS2013 says nothing:
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