Right. But that's just it. "musicPart" is an object. A noun. What the hell is a "Music Part"? It's a completely synthetic object you've had to create solely to namespace functions. It's like how so many large Java projects have static "Utils" classes.

What you've done is not OO; in fact, it's an anti-pattern in OO. You've created, as you correctly note, a namespace or module around static functions; there is no meaningful encapsulation of data.

My point isn't that it can't be done, it's that trying to follow best OO practices, you run into this sort of problem (which has had a lot of digital ink spilled on it). The fact there is a pragmatic solution isn't in any doubt; it's that such a solution intentionally eschews the data encapsulation that OO demands (but not imperative or functional approaches, which instead say it's the right approach to do that).

If you ever played music, you know it consists of parts. Say, a percussion part, a bass part, a rhythm guitar part, a lead guitar part, a vocal part, etc.

Why would 'play' hang off of the (presumably static) "MusicPart" then, rather than, "Player", "Musician", "Composition", etc?

Also, you realize that this whole discussion is proving the point, right?

But now the traits aren't connected with drums (or sticks) but MusicParts. Or you end up having some `drum.foo` too.