Re: # operator again... (sorry)

[Cosmin Apreutesei <cosmin.apreutesei@...>]

Varargs have limited size and are much slower than tables (I speculate
they were designed with the tuple concept in mind). With just tables
you can't iterate sparse arrays without a sort or hashing operation.
However, I'm fine with that, I don't need sparse arrays. I just wanted
contiguous arrays with known length to work with _any_ table, just
like ipairs() defines them for _any_ table. Right now I use the
iterator ipairs() gives me in a while loop just to get the
functionality of for i=2,#t. Btw, shouldn't inext() be exposed along
with next()?


On Thu, Jul 16, 2009 at 19:59, Jerome Vuarand<jerome.vuarand@gmail.com> wrote:
> 2009/7/16 Javier Guerra <javier@guerrag.com>:
>> On Thu, Jul 16, 2009 at 3:50 PM, Cosmin
>> Apreutesei<cosmin.apreutesei@gmail.com> wrote:
>>> Anything that could conflict with such changes?
>>
>> performance.   #t would decay into a O(n) operation
>
> And without a single change to Lua itself you can add support for
> sparse arrays with a couple functions:
>
> function pack(...)
>    return {['#'] = select('#', ...), ...}
> end
>
> local _unpack = unpack
> function unpack(t, i, j)
>    return _unpack(t, i, j or t['#'])
> end
>
> -- example
> local function foo(skip1, skip2, ...)
>    return pack(...)
> end
>
> print(unpack(foo(1, 2, 3, nil, 5, 6, nil, nil)))
> --> 3       nil     5       6       nil     nil
>
> If necessary you can even avoid putting the length in the array itself
> (in the example above at the key '#') with the help of a weak table.
>



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