None of these require macros.
If (and only if, I have not looked at our hypothetical model and fit GF, but for the sake of argument, I will assume that it does) "fit" specialises on "model" will a "mode = AnOtherModel" cause "fit(model, x, y)" to be exquivalet to Python's "model.fit(x, y)". If you need to provide a custom "fit" method, you do so by providing a method specialised on AnOtherModel to the "fit" GF.
At no point is there a macro involved.
As for the "module a, model nn" and "module b, model nn", I would naively assume that they actually are different models, and therefore something specialising on "a.nn" will not get dispatched to when you pass a "b.nn".
Disclaimer: I don't actually know Julia, at all. But I have written substantial amounts of CLOS code (and Python, but I like CL and CLOS better).
If (and only if, I have not looked at our hypothetical model and fit GF, but for the sake of argument, I will assume that it does) "fit" specialises on "model" will a "mode = AnOtherModel" cause "fit(model, x, y)" to be exquivalet to Python's "model.fit(x, y)". If you need to provide a custom "fit" method, you do so by providing a method specialised on AnOtherModel to the "fit" GF.
At no point is there a macro involved.
As for the "module a, model nn" and "module b, model nn", I would naively assume that they actually are different models, and therefore something specialising on "a.nn" will not get dispatched to when you pass a "b.nn".
Disclaimer: I don't actually know Julia, at all. But I have written substantial amounts of CLOS code (and Python, but I like CL and CLOS better).