swift - How to require that a protocol can only be adopted by a specific class

Question

I want this protocol:

protocol AddsMoreCommands {
     /* ... */
}

only to be adopted by classes that inherit from the class UIViewController. This page tells me I can specify that it is only adopted by a class (as opposed to a struct) by writing

protocol AddsMoreCommands: class {
}

but I cannot see how to require that it is only adopted by a particular class. That page later talks about adding where clauses to protocol extensions to check conformance but I cannot see how to adapt that either.

extension AddsMoreCommands where /* what */ {
}

Is there a way to do this? Thanks!

Answer 1

protocol AddsMoreCommands: class {
    // Code
}

extension AddsMoreCommands where Self: UIViewController {
    // Code
}