Re: Callbacks Again

From: William Kempf (sirwillard_at_[hidden])
Date: 2000-11-18 10:51:57

--- In boost_at_[hidden], Jesse Jones <jejones_at_a...> wrote:
> >On Fri, 17 Nov 2000 15:31:35 -0800
> >Jesse Jones <jejones_at_a...> wrote:
> But we know that we want to have some sort of empty test. If we do 
this
> with a bool or const void* conversion operator users will be able to
> compare any two callback objects, but in all probability this will 
return
> false unless you're dealing with the exact same callback on the 
left and
> right.

Actually, with the conversions in place comparisons will usually 
return true.  cb1 converts to a bool (likely true) and cb2 converts 
to a bool (likely true) and hence comparison likely returns true 
regardless if the callbacks are exactly the same.  (Actually, I'm 
quite tired while writing this and I'm not sure that the implicit 
conversions should occur in this case.  I'm fairly sure that if the 
callbacks are of the same type the conversion will not occur.)

> We can document that comparisons don't work as expected, but it
> seems better to arrange for a compile error if the user does 
something
> wrong.

That's simple.  You eliminate the comparison operations from the 
public interface (explicitly make them private).  It's then a 
compiler error to try and use them, which is the best idea 
considering we can't make them return useful information.

Bill Kempf