Re: Hi and pushing existing UserData from pointer

[delbu9c1@...]

Be careful. Lightuserdata all share the same metatable. This may not be your intent.

Lightuserdata does not create any kind of proxy. It is a pointer and that's it.

My approach to your problem would be to make a userdata the size of your pointer and then essentially use double indirection on any appropriate pointer you receive.

Matt
------Original Message------
From: Chris Camacho
Sender: lua-bounces@bazar2.conectiva.com.br
To: Lua list
ReplyTo: Lua list
Subject: Re: Hi and pushing existing UserData from pointer
Sent: Aug 16, 2009 9:49 AM

Im not too sure what you're getting at, however
I have found one answer....

   lua_pushlightuserdata(L, a);
   luaL_getmetatable(L, "cpShape");
   lua_setmetatable(L, -2);

does actually work! I'm getting userdata of the appropriate
type and if I add an impulse to the colliding shape the correct
body moves so the above *must* be passing a userdata reference
correctly, although what I suspect I'm doing is making a
dummy user data with the pointer inside ???

(This and some other "types" I'm going to remove from the
lua GC, in any case as it make more sense to pass back these
objects back to the library when you want to remove them
from the simulation)

Can you explain your method? can you provide a simple
code example that shows your technique working?

Best
Chris

Tony Finch wrote:
> On Sun, 16 Aug 2009, Chris Camacho wrote:
>   
>> Is there any way to make a new userdata that is a reference to an
>> already allocated userdata from just a C pointer?
>>     
>
> Create a weak table mapping lightuserdata to the full userdata. You can
> convert a C pointer directly to a lightuserdata which you can use to index
> the table. The table must have weak values so that your objects are still
> collected. Lightuserdata doesn't affect collection of the objects it
> points to.
>
> Tony.
>   


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