Re: How do you return multiple values?

[Geoff Leyland <geoff_leyland@...>]

Thanks Roberto,

On 5/11/2009, at 9:09 AM, Roberto Ierusalimschy wrote:

> > How do you return multiple values from a function that pcalls a  
> > function
> > that returns an unknown number of values possibly including nil in a
> > manner that doesn't involve undefined behaviour?
> >
> > [...]
> >
> > function b()
> >  local status, r = pcall(function() return { a() } end)
> >  if not r then error("nicely handled error!") end
> >  return unpack(r)
> > end
> >
> > [...]
>
>
> function pack (...)
>  return { n = select("#", ...); ... }
> end
>
> function b()
>  local r = pack(pcall(function() return { a() } end))
>  if not r[1] then error("nicely handled error!") end
>  return unpack(r, 2, r.n)
> end
>
> ?


Excuse me for causing confusion by writing "if not r" where I meant  
"if not status", and for the case of what I *meant*, it'd be

local status, r = pcall(function() return pack(a()) end)
if not status [...]

It has the advantage over Florian's that you only write pack once and  
you handle the error in b(), not in the helper function, whereas  
Florian's avoids the packing and unpacking.  I think they have the  
same number of closures?

Anyway, thanks to you both!

Cheers,
Geoff