Re: [sigc] Re: [Boost-users] Signals & Slots

[Martin Schulze <martin-ml hippogriff de>]

Am 07.01.2005 14:19:20 schrieb(en) Douglas Gregor:
> On Jan 7, 2005, at 6:12 AM, Murray Cumming wrote:
> > 3. In "Slot Binders"
> > Can you expand on this question: "TODO: answer questions: a) What's
> up
> > with the No Clue entry, anyone?", please. In fact, please just ask
> your
> > TODO questions on this mailing list.
>
> So the intent of retype() and retype_return() is to allow casting of
> the argument and return types of a function. Are these also required
> when performing implicit conversions? For instance, will the  
> following
>
> work?
>
>    long Func3(double val, string str);
>
>    sigc::signal<int, float, string> sig;
>    sig.connect(sigc::ptr_fun(&Func3));
>
> If I'm right in assuming that the code will not compile (because the
> signatures do not match exactly), then the "No Clue" could be  
> replaced
>
> by "Not Applicable", because
> Signals performs all of the implicit conversions.

I'm afraid, you're wrong here. Implicit conversions do work. retype 
(_return) is for explicit conversions.
However, using implicit conversions in libsigc++-2.0 without retype 
(_return) can cause troubles (at least warnings) with some compilers.

> > 4. Some of the "-ed" comments seem outdated now. It would be nice
> to
> > clean these up.
>
> Replying to some of the -ed comments:
>
>    - Regarding implementing the preferred syntax from Boost.Signals  
> in
>
> libsigc++: it should  be trivial, although support for writing
> function
> types is not as portable as we'd like.
>
>    - Regarding bloat factors: they're probably about the same in both
>
> libraries. The only thing we know to do to improve the situation is
> use
> function pointers instead of virtual functions, and to try to be
> careful about factoring our templates properly.

Well, I remember a benchmark posted some time ago ... :-)

>    - About ptr_fun/mem_fun: you can use them in either library, if
> you'd
> like to be more explicit.
>
>    - About bind: bind is now in the C++ Library TR (an addendum to  
> the
>
> standard, which should be approved in the near future), so we're
> forced
> to build on it to create any signals & slots library for the  
> standards
>
> committee. (We'll have a long, uphill battle if we try to introduce
> our
> own special binders and don't support bind).

Is there a way to deduce the return type of the bind functor object  
that is part of the TR? Will it be possible to "visit the targets" that  
are stored in the bind functor object with a function like  
Boost::visit_each() or sigc::visit_each()?

>    - Regarding libsigc++'s specialization for T_accumulator=nil: We
> don't need to discuss this in a standards proposal, because it's
> entirely a quality-of-implementation issue.
>
>    - Regarding Signals and Function: They don't play well together,
> but
> we're going to have to deal with this one way or another because
> Function is also part of the C++ Library TR.

I always thought that Boost had quite some influence on standard  
proposal? Who come that the TR is in a bad shape for a signal system,  
then?

> And one minor quibble: if we're going to explicitly qualify
> Boost.Signals by saying that it was strongly influenced by the work  
> of
>
> Karl Nelson (that's true), I think it's only fair to point out that
> libsigc++-2.0's interface was influenced by Boost.Signals.

No problem for me. The API was intended to be similar to Boost's. E.g.  
the accumulater API is borrowed from Boost.

Regards,

 Martin