Re: Feature request: userdata slice

[Philipp Janda <siffiejoe@...>]

Am 21.08.2015 um 00:21 schröbte Rena:
> On Aug 20, 2015 6:05 PM, "Roberto Ierusalimschy" <roberto@inf.puc-rio.br>
> wrote:
> > if we want to put some extra bits in
> > 'TValue' to good use and solve the OP problem, maybe a better idea would
> > be to introduce metatables for light userdata.
>
> That would be excellent. I find it difficult to find much real use for
> light userdata with only a single global metatable.

That would be another welcome feature, but lightuserdata pointing into 
full userdata is unsafe: the full userdata could be collected without 
the lightuserdata realizing/preventing that.

Btw., on 64 bit machines we have another 32 bits available due to 
padding (TValue is already 16 bytes there). It's only 32 bit machines 
where we'd have to deal with 24 bits or so.

> > (We could even gain individual metatables for numbers :-)
>
> So different metatable for 4 than for 5? That would be... interesting.

Since the metatable "pointer" would be stored in the TValue itself you 
could even have multiple numbers with value 4 on the stack and assign a 
different metatable to each.

Philipp