Classes or Structs

The second can be used for a class or a struct.

init<Subject>(_ subject: Subject, children: KeyValuePairs<String, Any>, displayStyle: Mirror.DisplayStyle? = nil, ancestorRepresentation: Mirror.AncestorRepresentation = .generated)

Interesting to note, here, is that you provide the children (i.e. properties) of your subject as a KeyValuePairs<String, Any> which is a bit like a dictionary only that it can be used directly as function parameters.