Re: Lua 5.2 - small enhancement for table.unpack

[Dirk Laurie <dpl@...>]

On Wed, Jun 29, 2011 at 11:27:24AM +0200, Matthew Wild wrote:
> On 29 June 2011 10:26, steve donovan <steve.j.donovan@gmail.com> wrote:
> > On Wed, Jun 29, 2011 at 11:20 AM, Patrick Rapin <toupie300@gmail.com> wrote:
> >> The function table.pack could also set a metatable with then __len
> >> metamethod returning the true length, since table.unpack already obey
> >> __len metamethod.
> >
> > That is a most elegant solution, I think.
> >
> 
> Until someone tries to modify the returned table and then wonders why
> the length doesn't change accordingly? :)
> 

That person could have done this:

t = table.pack(1,2,nil,4)
t.n = #t
getmetatable(t).__len = rawlen

thus obtaining the current solution.

I agree with Steve: Patrick's solution is elegant.  It exploits
a feature of Lua 5.2, whereas the current solution is reminiscent 
of older versions.

> getn (table)
> Returns the ``size'' of a table, when seen as a list. If the table has 
> an n field with a numeric value, this value is the ``size'' of the table. 
            — Lua 4.0 reference manual

Dirk