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It can often be quite a pain to use an index. From further up: > For example, in Rust, we often have to use an index or an ID where a regular reference would d

It can often be quite a pain to use an index. From further up: > For example, in Rust, we often have to use an index or an ID where a regular reference would do in Go. We need to do extra refactoring of function signatures to pass collections down the call stack so we can then use that index/ID... and then find we can't modify a function signature because it's a trait override, and resort to tricky workarounds. In Go, we just use a reference. That choice is decoupled from memory concerns. The problem is that you can't just dereference an index, you instead need all your callers' callers' signatures to take in the collection, causing a minor refactor shock wave in some cases. If that runs into an unchangeable signature (like a trait override, or a public API), it's pretty much game over and you're back to the drawing board. If you're making CLI program or small server, this might not hurt that much. In larger programs, the extra refactoring from this constraint can be quite costly and disruptive.

MrJohz 4y ago
I don't think I understand that example. If I understand correctly, the issue is the question of exclusive mutability, which is why you can't pass the mutable reference itself around. But for some reason you can pass around a mutable reference to the collection and an index? That seems surprising: theoretically, if you have a mutable reference to a collection, you can always transform it into a mutable reference to some subset of its children. Or is this a lifetimes issue, where the lifetime of the individual reference might be longer than the lifetime of the collection as a whole? In that case, it might be that the lifetime annotations aren't correct, or that the code is wrong in the first place. I get the idea that you can't change public APIs and function signatures, but that's true in pretty much every language.

MrJohz 4y ago

I don't think I understand that example. If I understand correctly, the issue is the question of exclusive mutability, which is why you can't pass the mutable reference itself around. But for some reason you can pass around a mutable reference to the collection and an index? That seems surprising: theoretically, if you have a mutable reference to a collection, you can always transform it into a mutable reference to some subset of its children. Or is this a lifetimes issue, where the lifetime of the individual reference might be longer than the lifetime of the collection as a whole? In that case, it might be that the lifetime annotations aren't correct, or that the code is wrong in the first place. I get the idea that you can't change public APIs and function signatures, but that's true in pretty much every language.