Re: Problem with userdata (metatable)

["Anders Bergh" <anders@...>]

I'm going to test what you did in your Delphi code, and test it in my
code to see if it works. How come the
http://lua-users.org/wiki/UserDataWithPointerExample example doesn't
work though? Did things change in Lua 5.1?

Anders

On 4/12/06, jdarling@eonclash.com <jdarling@eonclash.com> wrote:
> Since you in C/C++ take a look at how LUNA is doing things.  I'm no
> vertran myself, but I have had some problems with methods in Delphi
> (actually enough that I believe I see your problem).
>
> You need to track your methods table, object meta table, and object
> table.  For example some working code of mine (note again Delphi not C)
> is:
>
> procedure RegisterMyClass(LuaScript:TLUAWrapper);
> var
>   MetaTable,
>   MethodTable,
>   Methods : Integer;
> begin
>   lua_newtable(LuaScript.LuaState);
>   Methods := lua_gettop(LuaScript.LuaState);
>
> // Lua<#ClassName#>ClassName - represents the class name in text
>   luaL_newmetatable(LuaScript.LuaState, Lua<#ClassName#>ClassName);
>   MetaTable := lua_gettop(LuaScript.LuaState);
>
>   lua_pushstring(LuaScript.LuaState, Lua<#ClassName#>ClassName);
>   lua_pushvalue(LuaScript.LuaState, Methods);
>   lua_settable(LuaScript.LuaState, LUA_GLOBALSINDEX);
>
>   lua_pushliteral(LuaScript.LuaState, '__metatable');
>   lua_pushvalue(LuaScript.LuaState, Methods);
>   lua_settable(LuaScript.LuaState, MetaTable);
>
>   lua_pushliteral(LuaScript.LuaState, '__index');
>   lua_pushcfunction(LuaScript.LuaState, index_<#ClassName#>);
>   lua_settable(LuaScript.LuaState, MetaTable);
>
>   lua_pushliteral(LuaScript.LuaState, '__newindex');
>   lua_pushcfunction(LuaScript.LuaState, newindex_<#ClassName#>);
>   lua_settable(LuaScript.LuaState, MetaTable);
>
>   lua_pushliteral(LuaScript.LuaState, '__gc');
>   lua_pushcfunction(LuaScript.LuaState, gc_<#ClassName#>);
>   lua_settable(LuaScript.LuaState, MetaTable);
>
>   lua_newtable(LuaScript.LuaState);
>   MethodTable := lua_gettop(LuaScript.LuaState);
>   lua_pushliteral(LuaScript.LuaState, '__call');
>   lua_pushcfunction(LuaScript.LuaState, new_<#ClassName#>);
>   lua_pushliteral(LuaScript.LuaState, '__new');
>   lua_pushvalue(LuaScript.LuaState, -2);
>   lua_settable(LuaScript.LuaState, Methods);
>   lua_settable(LuaScript.LuaState, MethodTable);
>   lua_setmetatable(LuaScript.LuaState, Methods);
>
> // for each method that you want to register
>   lua_pushcfunction(LuaScript.LuaState, lua<#ClassName#><#MethodName#>);
>   lua_settable(LuaScript.LuaState, Methods);
> // end of for each method
>
>   lua_pop(LuaScript.LuaState, 2);
> end;
>
>  - Jeremy
>
> "Help I suffer from the oxymoron Corporate Security."
>
>
> > -------- Original Message --------
> > Subject: Problem with userdata (metatable)
> > From: "Anders Bergh" <anders@anders1.org>
> > Date: Wed, April 12, 2006 8:25 am
> > To: "Lua list" <lua@bazar2.conectiva.com.br>
> >
> > Hi!
> >
> > I'm using Lua 5.1 and I've been trying to add my own userdata type. It
> > works except I couldn't get methods working. I've been reading the
> > chapter in the first edition of pil and
> > http://lua-users.org/wiki/UserDataWithPointerExample.
> >
> > Here's the code I use:
> >
> > static const luaL_reg llua_user_f[] = {
> >   /* Functions */
> >   {"FindByNick", llua_user_FindByNick},
> >
> >   /* Methods */
> >   {"GetNick", llua_user_GetNick},
> >   {NULL, NULL}
> > };
> >
> > /* Metatable */
> > static const luaL_reg llua_user_m[] = {
> >   {"__tostring", llua_user_tostring},
> >   {NULL, NULL}
> > };
> >
> > int lluaopen_user (lua_State *L) {
> >   luaL_openlib(L, "user", llua_user_f, 0);
> >   luaL_newmetatable(L, TYPE);
> >   luaL_openlib(L, 0, llua_user_m, 0); /* mt */
> >
> >   lua_pushliteral(L, "__index");
> >   lua_pushvalue(L, -3);
> >   lua_rawset(L, -3);
> >
> >   lua_pushliteral(L, "__metatable");
> >   lua_pushvalue(L, -3);
> >   lua_rawset(L, -3);
> >
> >   lua_pop(L, 1);
> >   return 1;
> > }
> >
> > When I use "user:GetNick()" in Lua, I get the error: attempt to index
> > field '?' (a nil value).
> >
> > getmetatable(user) returns nil, tostring(user) returns "user:
> > 0x815598c". What exactly am I doing wrong?
> >
> > Anders
>
>