array slicing currently does not support steps?
simen.kjaras at gmail.com
Tue Aug 4 07:39:04 UTC 2020
On Monday, 3 August 2020 at 23:32:29 UTC, mw wrote:
> I just noted that D array slice does not support steps?
> Ever since Python 1.4, the slicing syntax has supported an
> optional third ``step'' or ``stride'' argument. For example,
> these are all legal Python syntax: L[1:10:2], L[:-1:1],
> L[::-1]. This was added to Python at the request of the
> developers of Numerical Python, which uses the third argument
>>>> L = range(10)
> [0, 2, 4, 6, 8]
> Shall we add a DIP for this?
Since D slices are just views of memory, this would either change
how slicing works (copy the data when using stride), or change
the memory layout of slices.
Currently, a slice is essentially a (ptr, length) struct, and
adding stride to the mix would require adding another field to
every slice. This would break all D code ever, so we can
disregard that solution.
Copying the data doesn't actually break any code, since the
no-stride case would be unaffected, and is the only case
currently in use. However, having a different behavior here would
break the principle of least astonishment.
Lastly, there's std.range.stride, which is an excellent
workaround with none of these drawbacks.
All in all, a DIP is very unlikely to be accepted given the above.
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