Re: C++ binding: arg errors

[Rici Lake <lua@...>]

On 7-Oct-06, at 2:16 AM, Nick Gammon wrote:

> On 06/10/2006, at 9:29 AM, Rici Lake wrote:
>
> > And for a good reason. If you remove the 'self' argument from the 
> > stack, and there is no other reference to it, then it could get 
> > garbage collected while your method is running, with possibly 
> > disastrous consequences.
>
> I'm trying to think how this would actually be a problem.
>
> I have taken the information from the self parameter and stored it (in 
> my case a userdata field) and then removed it from the stack, so I 
> don't want it any more. The called function doesn't want it, as it 
> never gets it in the first place.
>
> I suppose it could happen, if you called the function with a method 
> that was anonymously created on-the-fly, but it seems a strange way to 
> code to me.

It's not the method that is created on the fly, it's the object. 
Depending on your problem domain, that can be quite common:

-- Bignum arithmetic (part of DSA signature)

local r = key.base:exptmod(seed, key.p):mod(key.q)
local s = hash(digest):addmod(key.private:invmod(key. q):mulmod(r, 
key.q),
                              key.q)
                      :mulmod(seed, key.q)


-- Creating hierarchical structures:
w = Window()
w:attach(
   Menubar()
      :add(Menu"File"
             :add(Menuitem"New")
             :add(Menuitem"Open")
             :add(Menuitem"Close")
             :add(Menudivider)
             :add(Menuitem"Print")
          )
      :add(Menu"Edit"

-- etc