Re: SWIG and 0/1 based arrays

[Joey Mukherjee <joey@...>]

On Aug 7, 2008, at 1:12 AM, Mark Gossage wrote:

> I have recently had to go back to programming VB.Net and I have  
> been discovering that VB.Net is 0 based where VB6 was 1 based, its  
> a pain I agree.

VB?  Ooo, sorry to hear that!  :-)

> I certainly need to add some extra documentation on this matter,  
> but here is my thoughts on the matter.
> I wanted to keep wrappered vectors & wrappered C-arrays to follow  
> the same convertion that C does(0+), rather than convert to the Lua  
> convention (1+), as the underlying information is still C, not Lua.
> However if you convert from C-arrays to Lua tables, it makes more  
> sense for them to be numbered as Lua(1+).

With my code, I have a lot of gets and sets which operate on arrays  
(actually C++ vectors).  I would like a way to say within my .i file:  
"ok, everytime you (lua) access this array, subtract 1 from it before  
you call the C routine".  Basically, I want SWIG to generate these  
arg2-1's for me.

That said, I can see why someone might want a more natural C way,  
rather than Lua way, of accessing arrays.

Is there a way to make it an option in SWIG to do the -1's for me for  
every array access, or do I have write %luacode's for all my  
routines?   That would not be pleasant!  :-)

One more thing, is there a way to have SWIG/Lua do type-checking on  
bound data?  Here is what I am doing:

I have code that binds my C++ object to Lua which is as follows:

    lua_pushlightuserdata ((lua_State *) _LState, const_cast <void  
*> (ptr));
    lua_setglobal ((lua_State *) _LState, name);

Within my SWIG .i file, I have:

%typemap (in, checkfn="lua_islightuserdata") BOXLIST_P
%{
   $1 = ($type) lua_touserdata (L, $input);
%}
%typemap (in, checkfn="lua_islightuserdata") BOX_P
%{
   $1 = ($type) lua_touserdata (L, $input);
%}
%apply BOXLIST_P {QList <BoxPlots *> *};
%apply BOX_P {BoxPlots *};

In theory, I can send BOX_P and BOXLIST_P to each others function and  
cause my program to core.  Is there a way I can check that the Lua  
programmer sent the right type of variable to my wrapped function?

Thanks for all your hard work on the Lua module for SWIG!  I really  
enjoy having a nice alternative to C/C++ when messing with our data!

Cheers,
Joey