Go(lang): Robust generic functions on slices

>>signa1+(OP)
The problems with the API they point out are almost all things that rust's ownership system was built to solve.

Things like:

    slices.Sort(s) // correct
    slices.Compact(s) // incorrect
    slices.Delete(s, ...) // incorrect
    s := slices.Delete(s, ...) // incorrect if 's' is referenced again in the outer scope
    s = slices.Delete(s, ...) // correct

All of those are solved by having functions like 'slices.Sort' take a '&mut' reference in rust speak, and having 'slices.Compact' and 'Delete' take an owned slice, and return a new owned slice.

>>TheDon+IZ2
You don't even need a notion of ownership. A distinction between an immutable and mutable slice should be enough, because an immutable slice can never be changed which implies that its excess capacity (if any) can't be exploited for optimization.

>>lifthr+o13
None of these functions would apply to an immutable slice, so how is it related?

>>tsimio+I23
If immutable and mutable slices are differently typed [2], it is natural to define two functions (say, `slices.Compact` vs. `slices.Compacted`) to handle each type, like Python `list.sort` vs. `sorted`. It should be natural to expect `slices.Compacted` to never alter its input, and any attempt to use a mutable version will be very explicit except for slicing [1].

[1] Especially given that the capacity is preserved by default, which contributes to the current confusion. See my older comment: >>39112735

[2] Originally "...are different" but edited for clarity.

>>lifthr+k33
This would not allow the previous errors to be checked by the compiler since the main thing you're relying on is the name. Nothing prevents you to call deleted(mutable) and discard the result apart from the name.

>>makapu+b53
Indeed. Though, Rust does have a way to mark a function such that any caller that implicitly discards its return value gets a compiler warning. This feature largely solves the problem you’re talking about. But it’s orthogonal to Rust’s borrowing system or mutable versus immutable distinction.

That said, I’d also point out that, while you can more or less replicate the Go example with Rust slices, in Rust it would be more idiomatic to pass around a Vec (or a mutable reference to a Vec) if a callee needs to do something like change the length. And you can’t resize a Vec if there are other references to its contents.

zlacker