Is "for i in 1:length(A)" ever correct? Should Julia just emit a warning any time it encounters that pattern? Or maybe something slightly more complicated, such as that pattern followed by usage of i to index into A inside the loop?
In some rare cases, it very well might be exactly what the code's author intended and needed.
I tend to lean towards when Martin Fowler calls an "enabling attitude"[0] (as opposed to a "directing attitude") -- that is, when faced with a choice about how to design the primitives of an interface, I lean more often towards providing flexibility, and I try to avoid choosing ahead of time what users aren't allowed to do. It's better to document what's usually the wrong way to do something than to enforce it in the design. You can never guess what amazing things people will create when they are given flexible, unrestricted primitives.
So for cases like this, I think it's better to rely on a flexible linting tool (if available) than warnings or errors.
[0] https://martinfowler.com/bliki/SoftwareDevelopmentAttitude.h...
An issue was created sometime ago in StaticLint.jl to fix this: https://github.com/julia-vscode/StaticLint.jl/issues/337
Julia did not initially support arrays that aren't indexed from 1 (experimental support added in Julia 0.5, I don't know when it was finalised), and at that time I'm not even sure we had something like eachindex, certainly there would be no reason why someone would use it for an array.
Yes, actually. While I have approximately zero knownledge of Julia specifically, a language-independent example might be:
B = OneBasedArray(length(A))
A_ = iter(A)
for i in 1:length(A) { B[i] = pop(A_) }
assert(iter_isdone(A_))
> that pattern followed by usage of i to index into A inside the loop?
I can't think of any legitimate uses for that, but there probably are some; make sure to allow:
len = length(A)
for i in 1:len ...