Re: Overloading Library Functions in the Registry

[Eva Schmidt <es@...>]

Hello Thomas,

thanks for your mail. Just to make sure ..

> lua_getglobal(L, LUA_LIBNAME); -- get the table of the library
> lua_getfield(L, -1, "functionname"); -- get the old function
> lua_pushcclosure(L, function, 1); -- push the overloaded function
>                                   -- with upvalue to the old
> lua_setfield(L, -2, "functionname); set it to the library table
>
> So when your new function is called, you have the in an upvalue in the
> closure so you can retrieve it at index lua_upvalueindex(1) in the
> stack.

In this case I don't overwrite the old function but only make sure, that 
whenever the new function is called, the old is available vie the upvalue, isn't 
it? But I would need it the other way: When the old function is called, my 
function should also be called...

I need this actually to get notified of a certain event and put something into 
my own mainloop due to this. I strictly try to avoid to kludge the library code 
(with a hook) because of incompabilities to future library versions...

Eva

> Hope this help you
>
> Tom
>
> On Wed, Sep 05, 2007 at 12:11:11PM +0200, Eva Schmidt wrote:
> > Hello,
> >
> > I want to overload or extend an existing function (stored in the __index 
> > table) from a library. I want to do this from my C-program, NOT from Lua.
> >
> > Maybe I don't see the woods for the trees, but how can I access this 
> > metatable and manipulate a function in it?
> > I want to extend a certain function at the time of initializing (after 
> > opening the libraries) to connect this function call in Lua with a call of 
> > one of my own functions...
> >
> > I think it must be something like that:
> >
> >
> > 	lua_getglobal (L, LUA_LIBNAME); -- get the table of the library
> > 	lua_pushstring (L, "functionname") -- push the name
> > 	lua_pushcfunction (L, function) -- push the overloaded function
> > 	lua_settable (L, -3) -- set it to the library table
> >
> > ...
> >
> > I think this should overwrite the whole function with my own code. But I 
> > really want to extend the old function. Probably I need to call the old 
> > function from my new?!
> >
> > Maybe somebody has already done something like that and has some hints or 
> > ideas for me?
> >
> > Thanks a lot!
> > Bye
> > Eva

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