Question

I created a new VS “empty” project, and in it made a class. I decided to try this out as a library, went into properties and set the output type to class library. It compiles to a dll, though when I add it as a reference to another project, typing in “using …” doesn’t have my new library in there. If I create a new library project, past my class in there, compile that into a dll, then it works fine. So what I want to know is, what settings to I need to change in a blank project to get it to act as a dll?

Answer 1

using directives are about namespaces, not assemblies.

If your library is empty, it’s not contributing anything to a namespace, so a using directive won’t find anything.

It’s very important that you understand the difference between a namespace and an assembly – you could have library Foo.dll which only contains Bar.Xyz. You would add a reference in your project to Foo.dll, but a using directive for Bar.

As a more concrete example, the Enumerable class in the System.Linq namespace comes from System.Core.dll – but you still add the using directive for System.Linq, not System.Core. Indeed, if you try to add a using directive for System.Core, you’ll get an error – because that namespace doesn’t exist. (A namespace effectively doesn’t exist if it has no members.)