Re: [Boost-users] Connecting signals where one is a member

Subject: Re: [Boost-users] Connecting signals where one is a member
From: Frank Mori Hess (fmh6jj_at_[hidden])
Date: 2013-11-01 14:26:37

On Fri, Nov 1, 2013 at 1:04 PM, Chris Stankevitz
<chrisstankevitz_at_[hidden]> wrote:
> Hello,
>
> "Connect 4" fails to compile in the code below on g++ 4.6.3.
>
> Why does "Connect 4" not work while "Connect 2" does work?  Connect 4
> and 2 are the same thing as far as I can see.

bind behaves a little differently than you seem to be assuming when
dealing with pointers to data members, as opposed to pointers to
member functions.  Even though connect 2 compiles, it isn't doing the
same thing that connect 1 does. From the mem_fn docs (referred to by
the bind docs):

"mem_fn also supports pointers to data members by treating them as
functions taking no arguments and returning a (const) reference to the
member."

>
> Thank you,
>
> Chris
>
> #include <boost/signals2/signal.hpp>
>
> typedef boost::signals2::signal<void(   )> TDSignalA;
> typedef boost::signals2::signal<void(int)> TDSignalB;
>
> TDSignalA SignalA1;
> TDSignalB SignalB1;
>
> struct TSItem
> {
>   TDSignalA SignalA2;
>   TDSignalB SignalB2;
> };
>
> int main()
> {
>   TSItem Item;
>
>   // Connect 1
>   SignalA1.connect(Item.SignalA2);
>
>   // Connect 2
>   SignalA1.connect(TDSignalA::slot_type(&TSItem::SignalA2, &Item));
>
>   // Connect 3
>   SignalB1.connect(Item.SignalB2);
>
>   // Connect 4
>   //SignalB1.connect(TDSignalB::slot_type(&TSItem::SignalB2, &Item, _1));
>
>   return 0;
> }
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-- 
Frank