Re: Luabind and passing classes

You probably want to catch those, and print them out - or at least have a 
place you can put a debugger break point, and inspect the contents of 
luabind::error.  Sometimes the message will point you directly at the 
problem.  Othertimes, not so much. ;-)

Nigel
----- Original Message ----- 
From: "Nathaniel Lewis" <[email protected]>
To: <[email protected]>
Sent: Saturday, July 24, 2010 2:31 AM
Subject: Re: [luabind] Luabind and passing classes


> 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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