Extracting lambda expression from LINQ

Question

I have next chunk of code

var query = wordCollection.Select((word) => { return word.ToUpper(); })
                          .Where((word) =>
                                  {
                                      return String.IsNullOrEmpty(word);
                                  })
                          .ToList();

Suppose I want to refactor this code and extract the lambda expression from Where clause. In Visual Studio I just select this lambda and do Refactor -> Extract Method. By doing so I have my LINQ modified to

 var query = wordCollection.Select((word) => { return word.ToUpper(); })
                          .Where(NewMethod1())
                          .ToList();

and a NewMethod1() is declared as

  private static Func<string, bool> NewMethod1()
  {
      return (word) =>
      {
          return String.IsNullOrEmpty(word);
      };
  }

The question is why this new method does NOT have any input parameters, as delegate Func states that NewMethod1() should have a string input parameter?

Answer 1

To get the expected result, mark just this part String.IsNullOrEmpty(word) and Extract the method:

private bool NewMethod(string word)
{
    return String.IsNullOrEmpty(word);
}  

What you originally got is because the extract created a method that returns a delegate. Not a method that matches the delegate. It is a method that returns another method. The latter accepts a string parameter word and returns a bool result.

Sure doing the above changes your code to:

.Where((word) => NewMethod(word))

But you can safely change that to:

.Where(NewMethod)

Side Note:

No need to use the return keyword in your Linq Queries or any one-line lambda, you can refactor you query to be like this:

var query = wordCollection.Select(word => word.ToUpper())
                          .Where(word => string.IsNullOrEmpty(word))
                          .ToList();