Chambers wrote:
> Aren't Callback functions often used in places where it's not easy to 
> just change one thing and recompile?  I would think that many parts of 
> the codebase would depend on that specific function signature being the 
> way it is.

I would think if you have a callback routine that actually uses the third 
parameter, passing the right thing would be necessary each time, but you'd 
also have that information each time. I.e., you wouldn't be invoking the 
callback that depended on which controller was invoking it if it wasn't 
actually coming from the controller. Since the other routines didn't use 
that third parameter, they could get a dummy value there everywhere they're 
called from a context where the new parameter doesn't make sense.

I can see situations where that would be difficult to resolve, but you 
wouldn't be able to resolve it by passing the integer in cast to void* in 
those cases either.  I.e., given that they solved the problem by sometimes 
(i.e., conditionally) passing the value as the wrong type and then 
extracting it where appropriate, it doesn't seem like it's the sort of 
problem that would be hard to solve by adding a new variable of the right 
type (modulo performance problems and/or lacking some source code, of course).

If they were using a language where functions can have default arguments, 
this would the canonical example of "a good place to use that." :-)

-- 
   Darren New, San Diego CA, USA (PST)
   Understanding the structure of the universe
    via religion is like understanding the
     structure of computers via Tron.

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