Re: All values can have metatables (Was: Feature request: userdata slice

[Sean Conner <sean@...>]

It was thus said that the Great Daurnimator once stated:
> On 21 August 2015 at 19:33, Sean Conner <sean@conman.org> wrote:
> >   I do have a Lua module [1] where each userdata created gets its own unique
> > metatable.  I did that so I could associate additonal values at run time to
> > the userdata, like:
> >
> >         X = require "Xcore"
> >
> >         display = X.open_display()
> >         window  = display:window( ... I won't bore you with details here )
> >
> >         -- now add some additional values
> >
> >         window.comment = "This is the main window"
> >         window.child   = X.sub_window(...)
> >
> >   When a window (as a userdata) goes out of scope, the __gc method will
> > close the window and because each userdata gets its own metatable, the
> > metatable itself will be subject to garbage collection and thus any
> > resources (like windows, or fonts or anything else where the sole reference
> > is in that metatable) will be reclaimed as well.
> >
> >   This new method breaks that.  I'm not sure what I'm doing is *good* [1]
> > but it's a method that currently works.
> >
> >   -spc
> >
> > [1]     It wraps Xlib.  Not suitable for general consumption, even assuming
> >         anyone knows how to program to Xlib anymore.  It uses some
> >         questionable techniques [2] that I'm not sure should get out of the
> >         laboratory.
> >
> > [2]     No, really!  I'm be surprised if you could get the code to work on
> >         your machine.
> >
> 
> 
> Instead of giving each instance it's own metatable; use the
> 'uservalue' to associate a table with it.
> (see other thread from today: "lua_setuservalue() - what is it for?")

  I forgot to mention, this is in Lua 5.1.  On reflection, I probably could
have used lua_setfenv() but I didn't.  The task of changing (to use either
lua_setfenv() for Lua 5.1 or lua_setuservalue() for Lua 5.2/5.3 plus the
required changes to get those versions to work with the code base) has long
passed into the "daunting" area.

  -spc (Over 5,000 lines of C code already, and not all of Xlib is 
	supported ... )