Re: array size vs index of last element (was Re: setarray[unsetkey] doesn't trigger nounset in arithmetic context)

[Chet Ramey]

On 5/28/23 2:05 AM, Martin D Kealey wrote:
> On Tue, 23 May 2023 at 23:32, Chet Ramey <chet.ramey@case.edu> wrote:
>
> > On 5/22/23 10:56 PM, Martin D Kealey wrote:
> >
> > > For example, if one is filling an array in random order, rather than
> > > progressively adding to the end, then it is useful and makes sense to be
> > > able to ask the array for its highest index.
> >
> > You can parse the output of ${!array[@]} to get that.
>
> True, but stupidly inefficient for a large array. (If you're inclined to
> respond "but this is Shell so nobody cares about performance", please read
> my rebuttal in the PS below.)

I suppose that if I had a large array, that I was populating randomly
with sparse elements, and I was interested in the highest-numbered index,
and I deemed the usual way to discover the largest index too inefficient,
I would keep track of that at assignment time.


> How about making ${!array[@]:s:n} work in the obvious manner, including
> when s=-1 n=1?

I don't generally jam together two different parameter expansions to create
a hybrid one, but if you'd like to take a shot at it, send me what you come
up with.

Chet
--
``The lyf so short, the craft so long to lerne.'' - Chaucer
                 ``Ars longa, vita brevis'' - Hippocrates
Chet Ramey, UTech, CWRU    chet@case.edu    http://tiswww.cwru.edu/~chet/