[ithkuil]

yet it's clearly useful to have the concept of "the engine" even if you cannot drop it in any vehicle.

E.g. it's a clear boundary between teams that collaborate on the "car" system, it's something some engineers specialize in that is quite different from "suspension system" (and such knowledge can be carried across engine design instances).

But you're right, when we're talking about LEGO-style composability, as you said, it's about having pieces that fit together and can be rearranged in many ways, and the real world is far messier and rarely you have universal composability; there are instances of "bounded" composability; e.g. the tyres for my car likely fit many other similar vehicles, but not all.

[cgrealy]

>> yet it's clearly useful to have the concept of "the engine" even if you cannot drop it in any vehicle.

Absolutely! I'm not arguing against modularity at all. I think the concept of discrete subsystems interacting is pretty much universal (organs, components, rooms, streets).

>> there are instances of "bounded" composability; e.g. the tyres for my car likely fit many other similar vehicles, but not all.

Again, completely agree.

What I'm arguing against is uniformity of interface.

You wouldn't connect a tyre to a wheel the same way you would mount an engine to a chassis.

[ithkuil]

> What I'm arguing against is uniformity of interface.

> You wouldn't connect a tyre to a wheel the same way you would mount an engine to a chassis.

Yes, you're right, LEGO is extremely uniform, and no real system is _that_ uniform.

And even a uniform interface doesn't mean any combination makes sense.

Attaching a LEGO brick with wheels on the roof of a LEGO car is not different than soldering an axle on the roof of a car: technically possible but utterly useless.

Actually, soldering an axle on the roof of a car is composing uniform interfaces: atoms in chemical bonds form a finite set of building blocks too!