Lifetimes are viral in Rust because 1. you can't abstract over them, 2. affine types are viral by design, but generics themselves are anything but viral.

They're not viral in rust - you can always replace the generic with a concrete type in super types.

Well that's rather the point of being generic with any language, isn't it?

You can stop being generic when you have sufficient information to stop being generic. If you're writing a library, that can easily bubble up all the way to the top, because you may never have enough information.

ETA: I think I was using a definition of viral that wasn't entirely correct. I thought it was a casual term rather than a precise one. But it seems like you're saying something is viral if you _must_ pass it on. In which case I apologize, generics are "semiviral" (I'm trying to introduce this term - if it already exists & isn't this, I apologize) - you don't need to pass them on, there's just a tendency to. The result looks very similar.

Rust also has associated types, which are exposed to the implementer, but not to the consumer.

I mean, generics and associated types aren't equivalent, but they also are often exposed to the consumer. Eg, if you're accepting an Iterator, you'll want to populate the Item associated type.