title: How can I list all external classes that implement an interface in Visual Studio
body: <p>Imagine the following:
  You have an external library that you want to use and it isn't documented that well. You know that there is a class &quot;Parent&quot; with a method Add. Add takes an Object of the interface &quot;IChild&quot;.</p>
  <p>How can I list all classes, especially in that library, that implement this interface?
  (By that I mean visually in the editor not in code)</p>
  <p>I found some threads about this but none of them really answered my question. All of them were about listing your own implementations of an interface in your namespace (and that works fine for me).</p>
  <p>Just to make the problem clearer:
  Let me take the <a href="https://docs.microsoft.com/de-de/dotnet/api/microsoft.extensions.configuration.configurationbuilder?view=dotnet-plat-ext-3.1" rel="nofollow noreferrer">ConfigurationBuilder</a> from .Net core. The first thing I found about it in the internet is that I can call <code>new ConfigurationBuilder().Add(IConfigurationSource)</code>. Then I wondered how I can get an IConfigurationSource. My next step would be to google for the documentation or some examples on this platform. But I imagine that that's not the completely right way of doing things. I think you should be able to go to IConfigurationSource, and look through classes from the ConfigurationBuilder that implement this interface so that you can find it yourself. Always googling for examples or docs can't be the only way to go.</p>
  <p>(I use Visual Studio 2019 Community)</p>