When developing a framework other developers will use, we may need to include another framework to ours as a dependency. If we use the included framework just for the implementation details, we don't want it to be visible (re-export) to the developers that integrate our framework in their app.

That's why we need to find a way to “hide” internal dependencies from the clients of our framework. This is something that is being discussed over Swift Forums, and currently it's partly implemented, but Apple does not officially support it. It may introduce breaking changes in future versions of Swift.

We have three separate pieces that we will mention through the article.

We will do it manually with no dependency manager to make it transparent what we are doing.

And that would be it, right? Well, not exactly, let's export OurFramework.xcframework and try to use it from the test project. Xcode won't build the test project because it fails with the following error.

This time there are no errors and the project builds. But the problem is that now we can import included FrameworkA as well, which may not be behavior that we want.

If we want to hide the framework that is included in your framework as dependency for whatever reason we need to import the included framework differently. Instead of standard import FrameworkA we need to use @_implementationOnly import FrameworkA.

Now if we try import FrameworkA in the test project, Xcode will throw an error that it can't find the module FrameworkA. 

By using @_implementationOnly import, FrameworkA won't be added to the swiftinterface file.

Quote from Harlan Haskins from Swift forums post.