[sigc] Re: signals and copy constructors
- From: Martin Schulze <martin-ml hippogriff de>
- To: Antonio Coralles <noche suapie reflex at>
- Cc: libsigc-list gnome org, gtkmm-list gnome org
- Subject: [sigc] Re: signals and copy constructors
- Date: Tue, 04 Jan 2005 22:24:03 +0000
Am 04.01.2005 15:16:51 schrieb(en) Antonio Coralles:
Carl Nygard wrote:
> On Mon, 2005-01-03 at 23:46 +0100, Antonio Coralles wrote:
>> i know that this is more a libsigc++ question; but as gtkmm uses
>> libsigc++ heavily and the libsigc++ mailinglist is not very
populated i
>> ask this question here too:
>>
>> is there an elegant way to "change *p_obj in mem_fun(*p_obj,
...)"
>> after the signal is allredy attached to a concrete object , so
that
when
>> the copy constructor of that object is called,
some_signal.emit(...)
>> calls the method in the object created by this copy constructor
call ?
>> or is it better to think of a different design, so that this
question
>> doesn't come up ?
>>
>> to avoid misunderstandigs, here is somekind of example:
>>
>> //just a useless signal
>> sigc::signal<void> someSignal;
>>
>> //just a useless class
>> class Useless : public sigc::trackable
>> {
>> public:
>> void call_me() { ... }
>> };
>>
>> //a useless scope
>> ....
>> {
>> Useless u1;
>> someSignal.connect(sigc::mem_fun(u1, &Useless::call_me));
>> //ok now connected - but how can i automatically change the
target
>> object to u2 - so that u2.call_me() is called due someSignal.emit
()
?
>> Useless u2(u1); //imagine this call is made at a comletly
different
>> part in my programm - for example in a clone method ....
>> ....
>> }
>> ....
>
> This is a bad idea simply from the standpoint that C++ creates
temporary
> copies in a variety of situations, many of which you are not
consciously
> aware of. I'd find a different design.
>
> BTW, you can also disconnect the signal if you store the connection
info
> returned when you call connect(), so you can manually disconnect
and
> reconnect (so long as you have the original signal).
>
Well, i guess you are right, I should find another way, allthough
temporary copies aren't a problem, because i could make the copy
constructor private and use it only in a virtual clone method ....;
but
to store the the connection and the signal in the object to wich the
signal was connected seems messy and error prone.
I'm afraid that your initial idea is not supported by libsigc++2. You
would need a list of signals your object was connected to. This is not
available.
Regards,
Martin
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