Re: Support for negative index values in array fetching

On Jan5, 2011, at 15:17 , Pavel Stehule wrote:
> 2011/1/5 Florian Pflug <fgp@phlo.org>:
>> How so? You'd still be able to get the last element by simply writing
>> 
>>  array_relative(some_array, array[-1]).
>> 
>> Or, if we made the function variadic, by writing
>> 
>>  array_relative(some_array, -1).
> 
> Sorry, but It isn't too intuitive. Minimally for me. Why you don't
> thinking about simple functions with only positive arguments. There
> are only four combinations. I don't think we must have only one super
> function.
> 
> we need functionality for:
> 
> a) get first n items
> b) get items without last n items
> c) get last n items
> d) skip first n items

Now you've moved the goalpost - the OP wanted to access individual
elements, not slices! To support slices, a three-argument version
of array_relative() would be required, with the signature
 array_relative(some_array anyarray, first int[], last int[])

Your requirements (a) to (d) are then easily satisfied

a) array_relative(ary, array[0], array[n-1])
b) array_relative(ary, array[0], array[-n-1])
c) array_relative(ary, array[-n], array[-1])
d) array_relative(ary, array[n], array[-1])

The individual function approach might be a tad more readable for
one-dimensional arrays, but they don't scale well to the general
case.

Maybe the OP could comment on whether any of these solutions
would fit his needs?

best regards,
Florian Pflug