Re: [luabind] passing an pointer of an object instance created in c++ for a class bound using luabind (not using call_function i need to use plain lua_pcall)

[Tom M. <tom...@gm...>]

Kariem,

Assuming you have bound the class, and the module is loaded and bootstrapped
in the lua_State vm, this is perfectly legal and works great.  I do it all
the time.

The thing you need to think about is how you get a hold of the function you
want to call.  Here is a small sample from a project that extends some
trading infrastructure in  c++ into lua for fast trading model testing...

  // this is just normal luabind stuff registering the market (c++) class in
lua
  // and is how from lua people request a market data subscription ( an
async stream of realtime equity quotes )
  luabind::scope
  register_market()
  {

    using namespace trd;
    return lb::class_<trd::market>("market")
      .def( "get_market_data_subscription", &
market::get_market_data_subscription )
      .property( "current_time", & market::get_current_time )
      ;
  }

  ...
  // here we register an extra class written just to handle callbacks into
lua for market_data_subscriptions
  // its definition follows
  lb::class_<market_data_subscription_watch>(
"market_data_subscription_watch" )
    .def( lb::constructor<trd::market_data_subscription &,lb::object>() );

  // this class adapts a sigc++ callback with quote information to reach
into lua land
  // to a user defined callback
  class market_data_subscription_watch : public sigc::trackable
  {
  public:

    // it takes the c++ mkt data subsr. and a lua table where the key
'quote' points to a lua function
    // that takes one argument, quote object (also registered w/ luabind but
not shown here)
    market_data_subscription_watch( market_data_subscription &sub, object
table ) : m_lua_state( table.interpreter() )
    {

      // you need to make sure the table passed from lua isnt garbage
collected and we can't keep refs for it
      // so i place the table in our registry over the next several lines
      lua_pushlightuserdata( m_lua_state,  m_lua_state ); // the ptr to our
lua state will be the index of our ref table
      lua_rawget( m_lua_state, LUA_REGISTRYINDEX ); // now the registry
table for our module is on top of stack

      lua_pushlightuserdata( m_lua_state, this );  // we will put our stuff
indexed by the ptr to this :)
      table.push( m_lua_state );  // push the table for our callbacks so lua
won't gc the mfsob!
      lua_rawset( m_lua_state, -3 ); // now set the value in our fing table

      // this is just sigc++ stuff to have our c++ handle_quote( ) called
when a quote arrives
      sub.signal_quote().connect( sigc::mem_fun( this, &
market_data_subscription_watch::handle_quote ) );
    }
    ~market_data_subscription_watch()
    {
      // clean up of the mds requires releasing refs to the table so it can
be gc'd as needed
      lua_pushlightuserdata( m_lua_state,  m_lua_state ); // the ptr to our
lua state will be the index of our ref table
      lua_rawget( m_lua_state, LUA_REGISTRYINDEX ); // now the registry
table for our module is on top of stack

      lua_pushlightuserdata( m_lua_state, this );  // we will put our stuff
indexed by the ptr to this :)
      lua_pushnil( m_lua_state ); // nil out the entry
      lua_rawset( m_lua_state, -3 );
    }

    void
    handle_quote( const quote &q )
    {
      // the next several lines retrieve our lua table
      lua_pushlightuserdata( m_lua_state,  m_lua_state ); // the ptr to our
lua state will be the index of our ref table
      lua_rawget( m_lua_state, LUA_REGISTRYINDEX ); // now the registry
table for our module is on top of stack

      lua_pushlightuserdata( m_lua_state, this );  // we will put our stuff
indexed by the ptr to this :)
      lua_rawget( m_lua_state, -2 );

      // now the table passed into the constructor is retrieved
      object m_table( from_stack( m_lua_state, -1 ) );

      // sanity check to make sure it actually was a table
      if ( type( m_table ) == LUA_TTABLE )
      {
        // here i retireve the lua function from the table
        object func = m_table["quote"];

        // sanity check...make sure it is a function
        if ( type(func) == LUA_TFUNCTION )
        {
          finally call the lua function passing the quote
          try {
            func( &q );
          } catch ( const luabind::error &e ) {
            luabind::object err( luabind::from_stack( e.state(), -1 ) );
           TDEBUG( ACE_TEXT( "market_data_subscription_watch::handle_quote
failed: %s\n"), luabind::object_cast<const char *>( err ) );
         } catch ( const std::runtime_error &e ) {
           TDEBUG( ACE_TEXT( "market_data_subscription_watch::handle_quote
failed: %s\n"), e.what() );
         } catch ( ... ) { }
       }
      }
    }

  protected:
    lua_State *    m_lua_state;

  };


>From lua you have something like this:

-- some lua callback function that gets quotes
function my_quote_callback( quote )
  print (string.format( "WE HAVE QUOTE: %4.2f - %4.2f", quote.bid, quote.ask
) )
end

...
-- somewhere else in the code
-- assuming you have model already and is a luabind model object
mds = model:get_market_data_subscription( "JDSU" );
watch = market_data_subscription_watch( mds, { quote = my_quote_callback }
);

Now whenever a quote comes in, my_quote_callback will be called and as you
see in that function, it can happily access the quote objects properties,
methods, etc...

Hope this helps and wasn't too much...I was too lazy to write a stripped
down version.  Feel free to post more ?'s if you need.

-tom

On Sun, Jan 25, 2009 at 8:31 AM, Kariem mohmed abdel fattah <
kar...@gm...> wrote:

> Hi all,
> I want to know if possible to call a lua function using lua_pcall and lua's
> stack but passing to that function a pointer to an object of luabind bound
> class, and be able to call the bound methods on that object from lua
> function.
>
>
> c++:
> push(something);
> lua_pcall(L,1,0,0);
>
> lua:
> function testFunc(pointer)
>  pointer:someBoundMethod()
> end
>
> Thanks
>
> --
> Kariem
>
>
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