RE: a luaL_mapref with a map semantic ?

["Grellier, Thierry" <t-grellier@...>]

Well a C++ objet is a member of a pool and is allocated a table, by a pool allocator. And this is this pool allocator which dispatches to the pool member the table when an event occurs on it. The same way when an event occurs to the pool member it notifies the pool allocator which forwards the event to the table.
I'd like to keep this pool allocation management logic as independent as possible from a script. However using
But most important, I'd like to avoid to create a ref each time the pool member is allocated because this is either infinite growth or lot's of removing

-----Original Message-----
From: lua-bounces@bazar2.conectiva.com.br [mailto:lua-bounces@bazar2.conectiva.com.br] On Behalf Of Jerome Vuarand
Sent: Tuesday, September 19, 2006 11:56 PM
To: Lua list
Subject: RE: a luaL_mapref with a map semantic ?

If I understand well you have a C++ object that own a table. To keep a reference to the table, you put in the registry and keep the numerical index in the C++ object. And now from the table you want to find the C++ object that own it.
 
The way you do it is ok; but you only retrieve the numerical index (ref), not the C++ object. Instead you could put in the registry a pointer to your C++ object as a light userdata:

class Foo
{
public:
   Foo() : ref(0) { }
   int SetTable(lua_State* L, int index);
   int GetTable(lua_State* L);
   static Foo* GetObject(lua_State* L);
private:
   int ref;
};

// Take associated table from stack
int Foo::SetTable(lua_State* L)
{
   // Put table in registry
   lua_pushvalue(L, 1); // Duplicate table ref, use it as value
   this->ref = luaL_ref(L, LUA_REGISTRYINDEX);
   // Associate the table to this
   lua_pushvalue(L, 1); // Duplicate table ref, use it as key
   lua_pushlightuserdata(L, (void*)this); // Push this, us it as value
   lua_settable(L, LUA_REGISTRYINDEX);
   return 0;
}

// Push associated table on stack
int Foo::GetTable(lua_State* L)
{
   if (this->ref!=0)
   {
      // Get table from registry
      lua_pushvalue(L, this->ref);
      lua_gettable(L, LUA_REGISTRYINDEX);
      return 1;
   }
   else
   {
      return 0;
   }
}

// Find which object is associated to table on stack
Foo* Foo::GetObject(lua_State* L)
{
   // Get object from registry
   lua_pushvalue(L, 1); // Duplicate table ref, use it as key
   lua_gettable(L, LUA_REGISTRYINDEX);
   // gettable returned the light userdata corresponding to the C++ object
   return (Foo*)lua_touserdata(L, -1);
}

 
________________________________

De : lua-bounces@bazar2.conectiva.com.br [mailto:lua-bounces@bazar2.conectiva.com.br] De la part de Grellier, Thierry
Envoyé : 19 septembre 2006 06:31
À : Lua list
Objet : a luaL_mapref with a map semantic ?



Hello,

 

I've been using lua_ref as it is recommended to keep a reference to a table.

But my problem is that I'd like to find the C++ holder of the ref from another call. That is find which ref matches the table. I've been using this code: 

 

// find table

  lua_pushvalue(L, 1);

  lua_gettable(L, LUA_REGISTRYINDEX);

  int ref;

if lua_isnil(L, -1) {

// not found, create ref

    lua_pop(L, 1);

    lua_pushvalue(L, 1);

    ref = luaL_ref(L, LUA_REGISTRYINDEX);

// LUA_REGISTRYINDEX.table = ref

    lua_pushvalue(L, 1);

    lua_pushnumber(L, ref);

    lua_settable(L, LUA_REGISTRYINDEX);

} else {

// found : retrieve ref

    ref = (int) lua_tonumber(L, -1);

    lua_pop(L, 1);

}

 

But could it some better mechanisms ? And by the way does LUA_REGISTRYINDEX behaves as a weak table?