From: Ulrich Eckhardt (uli_at_[hidden])
Date: 2005-07-27 13:36:21
On Tuesday 26 July 2005 22:45, Rebooted wrote:
> In my program I need to store a map of signals, with an integer id
> corresponding to a signal in the map.
Some kind of map<id_type, signal_type>.
> Objects can request to be informed when another a specific message is
> emitted by connecting a member function to the signal in this map at
> the index corresponding to that message type.
IOW, objects can subscribe to events.
> However, since boost::signal inherits noncopyable, it cannot be stored
> in a map. What are the reasons for signal being noncopyable, and is
> there any chance this could be changed in the future?
(I'm walking on unknown grounds here, since I use libsigC++ instead, but last
time I looked, they were sufficiently similar - maybe some names are
different.)
The problem is that when you connect a slot to a signal, you get a reference
to that connection. Using that reference, you can also separate the
connection again. Now, what would happen when a signal was copyable? You
could end up with several connections, so which one would you disconnect?
Also, copying is not a trivial operation, so you'd rather avoid it.
Ideas:
Use Boost's function instead, which is copyable. Using bind, you can achieve
almost the same as with slots/signals. The exception is the automatic
disconnecting when the target object is destroyed, but that can also be
achieved by using weak_ptr and a wrapper function (maybe lambda would
eliminate even that).
Store a smart pointer instead of the signal itself. This would even speed up
operations on the map.
Uli