undefined | Better HN

0 pointsStefanKarpinski4y ago0 comments

Offset arrays aren't a kludge and the package would exist regardless of whether zero or one has been chosen as a default base for indexing. Having arbitrary index ranges in different dimensions is extremely useful in many application domains. When working with FFTs, for example, it's natural for the indices to be symmetrical around zero. Or when doing coordinate transforms like in this example from the excellent Images.jl package: https://juliaimages.org/stable/tutorials/indexing/.

0 comments

3 comments · 3 top-level

btilly4y ago

Offset arrays are a wonderful source of footguns, and this should have been obvious from the start. Either you train everyone to write loops in an official way that avoids the problem, or you are going to have bugs. And if you choose training, you have to train EVERYONE, because anyone coming in from another language will have the wrong habits.

Even Perl realized that changing the indexing of arrays was a bad idea. Which is why the special variable $[ has been deprecated every which way possible because it caused too many bugs.

StefanKarpinskiOP4y ago

Here's a post I wrote on Julia discourse about why one-based indexing is not the culprit here, no matter what people may feel about it aesthetically: https://discourse.julialang.org/t/offsetarrays-inbounds-and-....

Several of the most serious scientifically minded programming languages have also had arrays that can be indexed starting at different offsets, including Fortran, Chapel and Fortress. If Julia were zero-based OffsetArrays would still exist and be highly useful. OffsetArrays is not some "kludge" just to allow indexing from zero. Frankly, indexing from zero isn't improtant enough for that. What really makes OffsetArrays useful is being able to do things like have indices go from -k:k where k may depend on the particular dimension. That way the point A[0, 0, 0] is the center of the array and you can navigate up/down/back from there naturally. Of course you can simulate that with arrays that arrays that start at zero or one, but it's a major pain.

ShamelessC4y ago

Hubris

j / k navigate · click thread line to collapse