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class polymorphism in LUA

nekoflux · 2004-04-01T11:50:49

hey guys: I have several C++ classes which extend from a virtual class, and I want to be able to use the extended classes in LUA. How do I do this? Heres an example of what im trying to accomplish: My base class: class CMyBase{ public: CMybase(); virtual int someFunc() = 0; int a; }; My 2 classes extended from the base class: class CBox : public CMyBase{ public: CBox(); int someFunc(){ return a - 32; } }; class CSphere : public CMyBase{ public: CSphere(); int someFunc(){ return a + 14; } }; now heres my lua pseidocode: box = new CBox(); sph = new CSphere(); result_box = box:someFunc(); result_sphere = box:someFunc(); but for some reason this code crashes at runtime when I attempt to load the lua script. What am I doing wrong? I declare the module[] definition for all 3 classes, and it still doesnt seem to work..any ideas folks? thanks a lot!! neko [edited by - nekoflux on March 31, 2004 1:26:44 PM]

Engines and Middleware Programming

Started by nekoflux March 31, 2004 12:25 PM

10 comments, last by nekoflux 20 years, 3 months ago

XXX_Andrew_XXX

340

April 01, 2004 03:51 AM

Lua in combination with Luabind doesn''t really need the idea of a C++ base class. Don''t forget that in luabind you can try to call a method of an object which may or may not be there, but that method is *always* looked up a run-time.

Effectively Lua objects always exhibit virtual behavior, you can think of this as being similar to the concept of a vtable in C++, but rather than having a pointer based table, you''re dispatching to a function based on the name.

I''ve run the snippets that you''ve given in VC6 SP5 and VC7 and it builds (and runs) fine in both. Like Sneftel and Dew_LED I''m guessing that the problem''s with something else.

nekoflux

173

Author

April 01, 2004 11:50 AM

I fixed it. It was a combination of several things:

1) it didnt like the new operator, and the semicolons at the end were unneccessary

2) I had to declare the classes as extending the base class within the module definition. Heres the modue defines that accomplish this:

module(L)[	class_<CMyBaseClass>("CMyBaseClass"),	class_<CBox, CMyBaseClass>("CBox")        //register the virtual functions here for CBox,        class_<CSphere, CMyBaseClass>("CSphere")        //register the virtual functions here for CSphere];

Hope this helps someone in the future