Howto use metatables to expose C++ objects to LUA 5.0 and instantiate them using a multiplexed function?
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- Subject: Howto use metatables to expose C++ objects to LUA 5.0 and instantiate them using a multiplexed function?
- From: Ron Bakker <madrigal@...>
- Date: 2002年12月22日 15:59:22 +0100
Dear experts,
Recently I started investigating LUA starting with version 4.01. I
exposed C++ objects to LUA using:
int RegisterObject(lua_State *pState, const char *classname)
{
lua_pushcfunction(pState, &InstantiateObject);
lua_setglobal(pState, classname);
int newtag = lua_newtag (pState);
lua_pushcfunction(pState, &DisposeObject);
lua_settagmethod(pState, newtag, "gc");
m_tag2class.insert(make_pair(newtag, classname));
m_class2tag.insert(make_pair(classname, newtag));
...
}
The problem that I face is that I want LUA to be an auxillary scripting
engine outside of my game engine. So I defined global
'InstantiateObject' and 'DisposeObject' functions that try to lookup the
class for me. One problem arises here. When the InstantiateObject
function is called (corresponding potential 'a=Object{}' LUA code) I
sometimes can see that the name of the object I wish to create is within
the lua_State->Mbuffer. But off course this is the all-wrong method to
do it. I haven't found an other, for I don't comletely understand the
stack at that point.
int InstantiateObject(lua_State *pState)
{
const char * classToCreate = pState->MBuffer;
...
}
So, I wish to multiplex my class object creation. So I thought I'd have
a peek at LUA 5.0 and it's metatables. But I must say it still puzzles me.
Is there a simple example (or explaination of how the stack works for
c++ object registration) on how to use these metatables to implement a
object and register an Instantiation-callback?
Furthermore, on object instantiation, is there a way to retrieve the
metatable responsable for instantiation and derive the 'wanted' object name?
Please, your expert advice.
Regards,
Ron