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From: William Kempf (sirwillard_at_[hidden])
Date: 2000-11-17 18:03:36

--- In boost_at_[hidden], Jesse Jones <jejones_at_a...> wrote:
> >--- In boost_at_[hidden], Douglas Gregor <gregod_at_r...> wrote:
> >> On Fri, 17 Nov 2000 19:40:05 -0000
> >> 3) I have explicit classes (each derived from EventBase) which
> >> allow callbacks to member functions, free functions or
> >> functors. It appears that the William Kempf and Jesse Jones'
> >> solution would use only functors (relying on another library
> >> (the lambda library?) to build functors out of free/member
> >> functions).
> My (and I think William's version) handle free functions in the
same way as
> functors are handled. Member functions need a bit more. I think
they should
> be rolled into the core callback code, but William is so far

I think functors handle this. Every functor library has a way to
generate a "closure" form of functor. It seems wrong to duplicate
effort, especially when libraries specifically designed to addresss
this are likely to do a better job of it. However, I'm not hard
nosed about it, so give counter arguments for why they should be
> >> This makes it tougher to include the bool
> >> conversion (how do we know if a functor has a real target or
> >> not?), which I consider essential.
> >
> >The bool conversion can be handled by inclusion of a default
> >constructor that sets the "impl" pointer to null.
> Yep (of course a const void* conversion would be better than bool).

Would it? Didn't we decide the opposite for boost::any?
> >The actual functor
> >is an internal detail that does not effect this in any way. I find
> >it useful to leave things as they are in our implementation in
> >to not duplicate the effort of creating functors yet again. There
> >are already numerous libraries available for doing this, including
> >the standard library that comes with every compiler. Libraries
> >as Lambda do a much better job of this than we could possibly do
> >out duplicating a tremendous amount of effort, and with no clear
> >benefit.
> It's not a "tremendous amount of effort". :-) It's a bit tedious,
but it
> falls out very naturally from the code I posted.

I think we're crossing wires here. A closure is simple to implement,
at least minimally. However, libraries like Lambda do a better job
than the "minimalist" approach, and if you've looked at their
implementation you must agree that they are a "tremendous amount of
effort" :).

Bill Kempf

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