Why remove unused using directives in C#?

Question

There are a few reasons you'd want to take them out.

• It's pointless. They add no value.
• It's confusing. What is being used from that namespace?
• If you don't, then you'll gradually accumulate pointless using statements as your code changes over time.
• Static analysis is slower.
• Code compilation is slower.

On the other hand, there aren't many reasons to leave them in. I suppose you save yourself the effort of having to delete them. But if you're that lazy, you've got bigger problems!

I would say quite the contrary - it's extremely helpful to remove unneeded, unnecessary using statements.

Imagine you have to go back to your code in 3, 6, 9 months - or someone else has to take over your code and maintain it.

If you have a huge long laundry list of using statement that aren't really needed, looking at the code could be quite confusing. Why is that using in there, if nothing is used from that namespace??

I guess in terms of long-term maintainability in a professional environment, I'd strongly suggest to keep your code as clean as possible - and that includes dumping unnecessary stuff from it. Less clutter equals less confusion and thus higher maintainability.

Marc

In addition to the reasons already given, it prevents unnecessary naming conflicts. Consider this file:

using System.IO;
using System.Windows.Shapes;

namespace LicenseTester
{
    public static class Example
    {
        private static string temporaryPath = Path.GetTempFileName();
    }
}

This code doesn't compile because both the namespaces System.IO and System.Windows.Shapes each contain a class called Path. We could fix it by using the full class path,

        private static string temporaryPath = System.IO.Path.GetTempFileName();

or we could simply remove the line using System.Windows.Shapes;.

This seems to me to be a very sensible question, which is being treated in quite a flippant way by the people responding.

I'd say that any change to source code needs to be justified. These changes can have hidden costs, and the person posing the question wanted to be made aware of this. They didn't ask to be called "lazy", as one person inimated.

I have just started using ReSharper, and it is starting to give warnings and style hints on the project I am responsible for. Amongst them is the removal of redundant using directive, but also redundant qualifiers, capitalisation and many more. My gut instinct is to tidy the code and resolve all hints, but my business head warns me against unjustified changes.

We use an automated build process, and therefore any change to our SVN repository would generate changes that we couldn't link to projects/bugs/issues, and would trigger automated builds and releases which delivered no functional change to previous versions.

If we look at the removal of redundant qualifiers, this could possibly cause confusion to developers as classes in our Domain and Data layers are only differentiated by the qualifiers.

If I look at the proper use of capitalisation of anachronyms (i.e. ABCD -> Abcd), then I have to take into account that ReSharper doesn't refactor any of the Xml files we use that reference class names.

So, following these hints is not as straight-forward as it appears, and should be treated with respect.