Re: Luabind and passing classes

Nathaniel Lewis <[email protected]>
Newsgroups gmane.comp.lang.lua.bind.user
Message-ID <1279895462.23209.0.camel@XtremePC> 
It said exited on a run time exception. (luabind::error)
		Nathaniel

On Fri, 2010-07-23 at 15:42 +1200, Nigel Atkinson wrote:
> Really?  :-/
> 
> You first line should work!  What was the error you got?
> 
> Nigel
> 
> On Thu, 2010-07-22 at 07:03 -0700, Nathaniel Lewis wrote: 
> > Oh, I see.  The problem was in my Lua script (I just tried it).  I tried
> > to call:
> > 
> > print ("Lua: " .. obj:getSting())
> > 
> > That caused it to error.  However this worked.
> > 
> > local str = obj:getString()
> > print ("Lua: " .. str)
> > 
> > 				Nathaniel
> > 
> > On Thu, 2010-07-22 at 18:19 +1200, Nigel Atkinson wrote:
> > > Heh, I should have tried you code before I replied....
> > > 
> > > anyhow - using std:string will work, but I looks like const char *
> > > should work too.
> > > 
> > > I tried this using gcc -
> > > 
> > > #include <iostream>
> > > 
> > > #include "lua.hpp"
> > > #include "luabind/luabind.hpp"
> > > #include "luabind/operator.hpp"
> > > 
> > > class TestClass {
> > >     std::string myString;
> > > public:
> > >     TestClass() {
> > >         myString = "Not Initalized";
> > >     }
> > >     TestClass( const char* aString ) {
> > >         myString = std::string(aString);
> > >     }
> > >     void setString( const char* aString ) {
> > >         myString = std::string(aString);
> > >     }
> > >     const char* getString( void ) {
> > >         return myString.c_str();
> > >     }
> > >     void printString( void ) {
> > >         std::cout << myString << std::endl;
> > >     }
> > >     static void configureLuaObject(lua_State* lVM) {
> > >         luabind::module(lVM) [
> > >             luabind::class_<TestClass>("TestClass")
> > >                 .def(luabind::constructor <> ())
> > >                 .def(luabind::constructor<const char*>())
> > >                 .def("setString", &TestClass::setString)
> > >                 .def("getString", &TestClass::getString)
> > >                 .def("printString", &TestClass::printString)
> > >         ];
> > >     }
> > >     void callFunction(lua_State* lVM) {
> > >         luabind::call_function<void>(lVM, "AFunction",
> > > boost::ref(this));
> > >     }
> > > };
> > > 
> > > int main()
> > > {
> > >     lua_State* L = luaL_newstate();
> > >     luaL_openlibs(L);
> > >     using namespace luabind;
> > >     open(L);
> > > 
> > >     TestClass::configureLuaObject(L);
> > > 
> > >     if (luaL_dostring(L, "t = TestClass('My Test')\n"
> > > "print(t:getString())") == 1)
> > >     {
> > >         std::cout
> > >             << "Couldn't run Lua program: "
> > >             << lua_tostring(L, -1)
> > >             << std::endl;
> > >     }
> > > }
> > > 
> > > and it worked.
> > > 
> > > Nigel
> > > 
> > > On Wed, 2010-07-21 at 19:42 -0700, Nathaniel Lewis wrote: 
> > > > Thanks I spent a bit and got what I wanted working sort of.  How do you
> > > > you return strings from a exposed function?  I got the exposing working
> > > > fine and I can pass a string as a parameter but how do I get it as a
> > > > result. the class (part of testing) is
> > > > 
> > > > class TestClass {
> > > >     std::string myString;
> > > > public:
> > > >     TestClass() {
> > > >         myString = "Not Initalized";
> > > >     }
> > > >     TestClass( const char* aString ) {
> > > >         myString = std::string(aString);
> > > >     }
> > > >     void setString( const char* aString ) {
> > > >         myString = std::string(aString);
> > > >     }
> > > >     const char* getString( void ) {
> > > >         return myString.c_str();
> > > >     }
> > > >     void printString( void ) {
> > > >         std::cout << myString << std::endl;
> > > >     }
> > > >     static void configureLuaObject(lua_State* lVM) {
> > > >         luabind::module(lVM) [
> > > >             luabind::class_<TestClass>("TestClass")
> > > >                 .def(luabind::constructor <> ())
> > > >                 .def(luabind::constructor<const char*>())
> > > >                 .def("setString", &TestClass::setString)
> > > >                 .def("getString", &TestClass::getString)
> > > >                 .def("printString", &TestClass::printString)
> > > >         ];
> > > >     }
> > > >     void callFunction(lua_State* lVM) {
> > > >         luabind::call_function<void>(lVM, "AFunction",
> > > > boost::ref(this));
> > > >     }
> > > > };
> > > > 
> > > > getString throws an error when run.
> > > > 					Nathaniel
> > > > 
> > > > On Thu, 2010-07-22 at 13:40 +1200, Nigel Atkinson wrote:
> > > > > Hi Nathaniel,
> > > > > 
> > > > > Short answer: Yes.
> > > > > 
> > > > > If you bind a class using Luabind it can be passed to Lua functions as
> > > > > a parameter.  When you bind a class you do not need to bind the
> > > > > class's constructor.  Omitting the constructor prevents your Lua
> > > > > script from being able to instantiate that particular class, however
> > > > > Lua can otherwise use instances passed to it from C++.
> > > > > 
> > > > > I do this quite often with singleton classes.
> > > > > 
> > > > > Nigel Atkinson
> > > > > 
> > > > > On Wed, 2010-07-21 at 16:53 -0700, Nathaniel Lewis wrote: 
> > > > > > I was reading through some tutorials and I had a question unanswered.
> > > > > > How do I pass a specific class to Lua?  I have a class that represents a
> > > > > > world in my game engine and I need some way to talk with it from Lua.  I
> > > > > > think LuaBind is the answer but I don't know.  I would never want to
> > > > > > create the class from Lua.  Instead I would want to pass a reference to
> > > > > > the one created on the c++ side to Lua and then call functions inside of
> > > > > > it.  Is this possible with LuaBind?  Basically a simple script would
> > > > > > look like this
> > > > > > 
> > > > > > -- called when map is loaded by engine --
> > > > > > function Init (worldInstance) 
> > > > > >     -- do stuff --
> > > > > > end
> > > > > > 
> > > > > > -- called after every frame is rendered --
> > > > > > Update = coroutine.wrap( function (worldInstance, timeSinceLastFrame)
> > > > > >     while true do
> > > > > > 	-- do stuff + call coroutine.yield() when waiting for things --
> > > > > >     end
> > > > > > end)
> > > > > > 						Nathaniel
> > > > > > 
> > > > > > 
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