[Boost-users] Signals & Slots

From: Foster, Gareth (gareth.foster_at_[hidden])
Date: 2004-11-17 09:20:19

Hello,

I was just reading some mention of bugs in boost::signal, is this
implementation in competition with libsigc++? i.e. does it aim to do the
same job, but under a different license, or is there perhaps some
fundamental design difference between the two?

Maybe it's a totally unrelated library (it doesn't look that way, but still
...). Either way, thank you for any information.

Regards

gaz

-----Original Message-----
From: boost-users-bounces_at_[hidden]
[mailto:boost-users-bounces_at_[hidden]] On Behalf Of Nat Goodspeed
Sent: 17 November 2004 13:39
To: boost-users_at_[hidden]
Subject: RE: [Boost-users] Signal with return value will crash

> -----Original Message-----
> From: boost-users-bounces_at_[hidden] [mailto:boost-users-
> bounces_at_[hidden]] On Behalf Of WangYun
> Sent: Tuesday, November 16, 2004 10:03 AM
> To: boost-users
> Subject: [Boost-users] Signal with return value will crash
> 
> I tried the signals, the code below will crash
> 
> #include <boost/signal.hpp>
> int _tmain(int argc, _TCHAR* argv[])
> {
> 	boost::signal<int(int)> _sig;
> 	_sig(10);
> 
> 	return 0;
> }
> 
> but code below works well
> 
> #include <boost/signal.hpp>
> int _tmain(int argc, _TCHAR* argv[])
> {
> 	boost::signal<void(int)> _sig;
> 	_sig(10);
> 
> 	return 0;
> }
> 
> The only difference is one has return value, the other doesn't, is
this a
> bug or by design?

[Nat] The difference between a void slot and one with a return value is
that in the latter case, the signal needs a combiner to figure out what
to do with multiple returns from multiple slots. See:

http://www.boost.org/doc/html/ch06s02.html#id2520177

I haven't actually tried your example, but it looks to me as though the
default combiner isn't working for you. But then you probably want
something other than the default anyway -- unless you don't care about
the values returned by your slots -- in which case why not use void
slots?

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