Re: Lua 5.2 - small enhancement for table.unpack

[Lorenzo Donati <lorenzodonatibz@...>]

On 30/06/2011 5.10, Daurnimator wrote:
> On 30 June 2011 01:29, Lorenzo Donati<lorenzodonatibz@interfree.it>  wrote:
> > Mmm, but what's the use of pack, then?
> >
> > > local t,t_n = table.pack(...)
> >
> > you can write also in 5.1.4:
> >
> > local t,t_n = {...}, select('#',...)
> >
> > and it isn't much more verbose.
> >
> > table.pack is useful as it is because it is very short in the common case of
> > storing away all the vararg info in one shot (with n, so it handles possible
> > nils).
> >
> > Perhaps, table.pack could still return n as a second argument, but the
> > injection of n in the table is very useful IMO.
> >
> > > print(unpack(t,1,t_n))
> > >
> > > Daurn.
> >
> > cheers
> > -- Lorenzo
>
> The purpose of bringing back  table.pack is to make it so that doing 2
> vararg related operations doesn't have to happen; apparently they are
> quiet expensive: so table.pack is introduced where it figures out the
> length and packs a table all at once.

Ok, so returning the length as a second argument is a good idea, indeed. 
But the injection of n in the table is good too. They are two different 
use cases. table.pack could support both.

Is it really a problem to have the table returned by table.pack contain 
n? If you really don't want it, it is easy to write:

t, n = table.pack(...)
t.n = nil

I think that it is also a bit more efficient than write:

t, n = table.pack(...)
t.n = n

this latter may trigger a rehash in the current implementation (but 
these are really implementation details).

-- Lorenzo