Go(lang): Robust generic functions on slices

Re:Go(lang): Robust generic functions on slices by errnoh on Saturday February 24, 2024 @07:53AM (#39491152)

Possibly that's mostly out of familiarity with the language? The only thing in your example that does things in-place (and thus looks out-of-place) is Sort(), but that's the way I'd at least expect it to work? If you take that away from the list all of them behave similarly to each other and return the modified slice:

    slices.Compact(s)       // modified slice in the return value is ignored
    s  = slices.Compact(s)  // s now points to the new changed slice
    s := slices.Compact(s)  // s already exists, this is not valid Go syntax.
    slices.Delete(s, …)     // modified slice in the return value is ignored
    s = slices.Delete(s, …) // s now points to the new changed slice

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Re:Go(lang): Robust generic functions on slices by masklinn on Saturday February 24, 2024 @08:01AM (#39491190)

> The only thing in your example that does things in-place (and thus looks out-of-place)

That is not really correct, and is much of the issue: Compact and Delete operate in-place on the backing buffer while copying the slice metadata. This is the same issue as the append() builtin and why it's so fraught (before you get in all the liveness stuff).

> s := slices.Compact(s) // s already exists, this is not valid Go syntax.

    s := []int{}
    if true {
        s := slices.Compact(s)
        _ = s
    }

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Re:Go(lang): Robust generic functions on slices by errnoh on Saturday February 24, 2024 @08:47AM (#39491449)

Ah, my bad for not reading the article before the comments :)

As that's the case it's indeed hard to defend it. Data structure-wise it still kind of makes sense since as you mentioned the slice metadata is changed, but it basically making the old slice invalid is rather annoying.

For the := example sure, it's a bit far fetched example and likely would not pass any code review, but there are cases where shadowing is indeed valid. So is the `s := slices.Compact(s)` in this example not working as expected then?

EDIT: looking at another reply to the parent the := being broken likely is trying to point that using := also modifies the slice and thus the original slice is broken when one tries to use it in the original scope. That's really bad practice, but true indeed.

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