[steveklabnik]

Yeah, you have to get into all of these details to have a productive conversation. Likewise, I don't actually think a lot of this inherently has to do with performance, basically, I could make a similarly lengthy comment about how

> I kind of think no, primarily that it is a performance consideration that infects the API and spreads everywhere; it's a distraction.

is something I fundamentally disagree with; unfortunately, I don't really have the time at this moment to even get it into the level that you have here, but it's a good conversation to have, and a needed level of details to even have a good conversation.

[brundolf]

Seconding the disagreement with the idea that mutability tracking is a distraction. I would give anything to have true deep-immutability enforced by TypeScript, but unfortunately the language semantics make it virtually impossible. In Rust, it might be my favorite feature.

[titzer]

Interesting. We definitely should have this conversation in the proper detail, because my estimates of Rust's language design priorities must be off.