Re: native converter questions

On Mon, 17 Aug 2009 12:25:51 +0200
Kristoffer Danielsson <[email protected]> wrote:

> What's wrong with this?
> 
> v1 = Vec2(1,2)
>  
> All you have to do is to bind a constructor of type (int, int).

You still won't be able to do :
  t = {1,2}
  v1 = Vec2(t)
  do_stuff(t)
  do_stuff{1,2}

(and see my remark in first post about having to write thin
wrappers for each and every function similar to do_stuff).

Besides Vec2 was only an example; The point is to allow native
conversion from/to lua tables without modifying the c++ code.  Maybe a
second example could make things clearer? Consider a 4x4 matrix. The
c++ class will probably have a constructor from float*, which you'll
want to convert to a constructor from table. Adding a custom
constructor taking 16 float parameters is out of the question:

- you'd have to change the c++ library (unless you know a way to
  do this outside of the matrix class?)

- such a constructor could not be bound with a standard build of
  luabind (which accepts 10 parameters max IIRC).

- this still would not allow the usage I'm looking for.


-David


> > Date: Mon, 17 Aug 2009 11:49:50 +0200
> > From: [email protected]
> > To: [email protected]
> > Subject: [luabind] native converter questions
> > 
> > Hi,
> > 
> > Suppose you have a class vec2, and a function do_stuff(const Vec2&).
> > I'd like to have native converters between vec2 and lua tables, so I
> > could write for example :
> > 
> > v1=Vec2{1,2}
> > do_stuff{x,y}
> > 
> > I specialized luabind::default_converter<Vec2> to achieve this,
> > which worked, except that I can not use my vec2 bindings anymore,
> > e.g :
> > 
> > =v1
> > error calling 'print' (No matching overload found, candidates:
> > void __tostring(lua_State*,Vec2 const&))
> > =v1.x
> > No matching overload found, candidates:
> > custom [f] <unknown>(Vec2 const&)
> > 
> > (both worked before I wrote the native converter). Does anyone see
> > what I did wrong? I can give more details if needed.
> > 
> > As an alternative, I thought of writing "light wrappers" instead of
> > custom converters, but this lead me to 2 problems:
> > 
> > - I have a couple of classes like vec2 above, and a lot of functions
> > that take them. I'd need to write wrapper functions (taking
> > lua tables) by-hand, for all of them. That's going to be painfull to
> > write, review and maintain.
> > 
> > - I could not find a way to simulate a custom constructor allowing
> > to write e.g v1=Vec2{x,y}
> > (without touching the original c++ api that is). The closest I got
> > to was adding pseudo class-methods acting like factories:
> > v1=Vec2.New{x,y}
> > 
> > Is there a better way? Thanks!
> > 
> > - David
> > 

------------------------------------------------------------------------------
Let Crystal Reports handle the reporting - Free Crystal Reports 2008 30-Day 
trial. Simplify your report design, integration and deployment - and focus on 
what you do best, core application coding. Discover what's new with 
Crystal Reports now.  http://p.sf.net/sfu/bobj-july