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



On Jan 10, 2005, at 1:48 PM, Peter Dimov wrote:

Doug Gregor wrote:
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?

I wouldn't say that it is in bad shape for a signal system. The
problem with {boost:: or tr1::}function and a signals system is that
they both do the same thing: erase the static type of a function
object so that it can be called through an entity that does not
encode that type. The problem is that we need to call visit_each
before we erase that type: 'function' shouldn't do it all the time,
because that could be costly, and the signal/slot can't do it because
the type is gone.

I still think that we need to explore the alternative approach of storing a weak_ptr in the function object and make the signal automatically disconnect on bad_weak_ptr. This ties automatic disconnection to shared_ptr+weak_ptr, but now they are part of TR1.

This is still a really good idea, and we should support it.

The upside is no base classes and no visit_each.

The downside is that you have to use shared_ptr + weak_ptr. Granted, that's a pretty common use case.

I'm not sure whether this line of thought should be continued to its natural conclusion, making the signal disconnect on any exception, not just bad_weak_ptr. bad_function_call, for example, is an obvious candidate. What is the current course of action when a slot throws?

The exception is propagated to the combiner (Boost terminology; it's accumulator in libsigc++), which may intercept it. The default combiner propagates it back to the signal caller.

	Doug




[Date Prev][Date Next]   [Thread Prev][Thread Next]   [Thread Index] [Date Index] [Author Index]