Mimic luabind behavoiur

[DJYar]

Hello everyone!
I have some troubles implementing script engine inside game engine port from C++ to C#.
Original game uses luajit + luabind. There are scripts which are implementing UI, AI and some other entities.
Also it is possible to define own system, register callbacks and game engine will call them from its main loop (or when any specific event will occur).
I can't make changes in any of bundled scripts but can make some sort of preprocessor.

To export classes from native side I've copied binding example from this Issue and upgraded it a bit (using luabind sources as a reference).
I had to make a helper class to be able to call either native or overloaded methods in script-registered class.
Luabind class "" () syntax works somehow, also super() for constructor.

Main issue is to make calls to base native or scripted class. For example

class "TestClass" (NativeClass)

function TestClass:OverridedMethod()
    return -NativeClass:OverridedMethod()
end

or even

class "TestClass2" (TestClass)

function TestClass2:OverridedMethod()
    return -TestClass:OverridedMethod()
end

This tricky thing is made with upvalues in luabind but we have no upvalues in NeoLua so I have no idea how to mimic this behaivour.

Current messy script engine prototype is here in gist

Thanks in advance.

[neolithos]

Why no using debug.getupvalue?

But overall, I do not really understand the question. What code is generated with class "" ()?

[DJYar]

Hey, thank you for the answer. I'll try to describe luabind flow with my lame english (sorry about that 😢)

Function class("TestDerived") creates class representation object on the native side and creates globally visible table TestDerived. Also at this point luabind creates metatable for TestDerived table with object construction dispatcher (__call) and other utility things in it.

Then function returns another function (stage 2) which takes base types as an arguments. This stage2 function is copying base's metatables to class rep, updates global class registry and type cast graph and defines super() member that is visible only inside __init() function of derived class instance. Very common pattern is function TestDerived:__init() super() --[[ ... ]] end

Also it is possible to call base member by its explicit type name. For example

function TestDerived:Sum(a, b)
    return BaseClass:Sum(a,b)
end

So it sounds like super() and all base classes are upvalues or I have to setfenv somehow.

I'm trying to port luabind class_rep/object_rep from here but without class registry, cast graph, GC handling etc etc but I think that it will be impossible to do such complex thing without Lua VM api

[neolithos]

I'am also not a native speaker ;-).

The class initialization and the metatable stuff works fine within plain (Neo)Lua.

As I understand the class_rep.cpp. It create a new stack and code in the lua-machine. This is at this point not possible in NeoLua (compiled is compiled). But you can change the compile result by implementing your own ILuaDebug. This implementation can catch the class("TestDerived") call or the __init (to introduce a local variable super).

In this part you have all freedom to change everything.

[DJYar]

Sounds good, I'll look into it, thank you! I'll post my research results here later ;)