Re: Assign a C++ function to a global lua variable

Here is my current function to overwrite the global metatable (doesn't seem
possible to create a metatable per type_id) , everything is ok it works (I
put it there for other people interested):
bool
CLuaVM::setSpecialNewIndex(){


    luabind::detail::class_registry* reg  =
detail::class_registry::get_registry( _vm );
// with templates you could possibly set a metamethod per class_rep, but
right now any type actually registered can be used to access the generic
metatable
    luabind::detail::class_rep* rep = reg->find_class(
typeid(irr::SIrrlichtCreationParameters) );

    if(!rep){
        _LOG_WARNING << "could not find a class re for this type";
        return false;
    }
    else {
        _INFO << "found rep for class '" << rep->name() << "'";
    }
    int index = rep->metatable_ref();


    // voici la cle utilise pour acceder au tableau representant la
metatable
    lua_pushinteger( _vm, index );
    // Pushes on top of stack the metatable
    lua_gettable(_vm, LUA_REGISTRYINDEX);
    lua_pushstring( _vm , "__newindex");
    //   Here I set my own __newindex function replacing the default one aka
class_rep::lua_settable_dispatcher
    lua_pushcclosure(_vm, &onNewIndex, 0);
    lua_rawset( _vm, -3);

    // pop metatable
    lua_pop( _vm,1);
    return true;
}

In fact for the moment my onNewIndex function is exactly the same as the one
provided by default (I put it so that you don't have to look for it)
int onNewIndex(lua_State *L) {

    //If the value at the given acceptable index is a full userdata, returns
its block address. If the value is a light userdata, returns its pointer.
Otherwise, returns NULL.
    detail::class_rep* crep =
static_cast<detail::class_rep*>(lua_touserdata( L, 1));


    crep->get_table(L);

    // copy key, then value
    lua_pushvalue(L, -3);
    lua_pushvalue(L, -3);
    lua_rawset(L, -3);

    // pop table
    lua_pop(L, 1);

    // get default table
    crep->get_default_table(L);
    lua_replace(L, 1);
    lua_rawset(L, -3);

    return 0;
}


This function __newindex is called on the only line of my script
"config.lua" which is:
EngineConfig.DriverType  = 5;

EngineConfig is a global registered from C++ (everything works if I don't
change the luabind metatable):
    luabind::object globals;
    script.getGlobals(globals);
    globals["EngineConfig"]     = &engineParam;

The call to my personalized __newindex function crashes because
crep->get_table(L);  and crep->get_default_table(L); both push nil on the
stack instead of tables. Why is that ?

I know this is a long mail but if you could give me a hint please. I've
already spent a lot of time on this.

matt

nb : Here is how I bind things:

luabind::class_<irr::SIrrlichtCreationParameters>("SIrrlichtCreationParameters")

.def_readwrite("DriverType",&SIrrlichtCreationParameters::DriverType)
        .enum_("DriverTypes")
            [
                value("opengl", video::EDT_OPENGL),
                value("directx8",video::EDT_DIRECT3D8),
                value("directx9",video::EDT_DIRECT3D9),
                value("software",video::EDT_BURNINGSVIDEO)
            ]



On Thu, May 26, 2011 at 1:11 AM, Teto <[email protected]> wrote:

> Hi folks,
>
> I want to overwrite the __newindex method for a certain type of class from
> the C++ side (to prevent creation of new properties without me noticing it,
> it prevents me from mistyping variables).
>
> Here is as far as  I go:
> bool
> CLuaVM::setSpecialNewIndex(const char* class_name){
>
>     luabind::object obj = get_class_names( getVM() );
>     luabind::object mt = getmetatable(obj[class_name]);
>
>     mt["__newindex"] = specialNewIndex; // specialNewIndex should be the
> function called when __newindex is called from lua for that class
> }
>
> It's late here so maybe that's why I miss something.
>
> Matt
>

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