Re: [PATCH] make light userdata a little bit heavier

[Ross Bencina <rossb-lists@...>]

On 22/04/2014 5:14 PM, Coroutines wrote:
> On Tue, Apr 22, 2014 at 12:09 AM, Philipp Janda<siffiejoe@gmx.net>  wrote:
>
> > > >>What I gain is the ability to verify the type safety of light userdata
> > > >>usage on the C side
> Ahah!  I get what's going on ITT now. :-)
>
> Maintain a vector of addresses that are copies of the lightuserdata
> for the particular type you're checking for.  Keep it sorted for
> binary-searching it later.  Not as light as what you're suggesting,
> but it wouldn't require modifying Lua if this proposal doesn't get
> accepted :>

Yep, or a hash table.

Or you could use spare bits of the C pointer as was suggested earlier.

Or if your objects are allocated from a slab you can do a pointer range 
check.

Sorry to change my tune, but more and more I am thinking that the killer 
feature of this patch is the ability to have multiple classes of light 
userdata each with their own metatable. This allows operator overloading 
for a particular class. Which would be neat if one of your light 
userdata happened to have algebraic structure.

Ross.