Re: light userdata (Was: Fastest way to transfer data from C to Lua ?)

[Philipp Janda <siffiejoe@...>]

Am 09.06.2013 17:26 schröbte Kevin Martin:
> On 9 Jun 2013, at 12:05, Tim Hill wrote:
>
> > so it is of limited use unless the pointer is to static memory or heap memory that will not be released until after the Lua state is closed. I'm with you.
>
> This isn't true if the light userdata are stored in a table which has a gc metamethod to call the appropriate free function.
>
> I hardly ever use full userdata as an object, but instead use a table and put light userdata in it. I find it much more flexible than full userdata.

But then you need to maintain a set of valid userdata handles for each 
class to make it safe, or else:

    do
      local o1, o2 = class1.new(), class2.new()
      o1.udata, o2.udata = o2.udata, o1.udata
    end
    collectgarbage()
    collectgarbage()
    -- boom

... and __gc for tables only works in Lua 5.2 and up.

> Kevin

Philipp