Re: [sigc] bind arguments within mem_fun()

[Martin Schulze <martin-ml hippogriff de>]

Am 01.09.2004 15:50:51 schrieb(en) Andreas Matthias:
> Is it possible to bind an argument to a function that is referenced
> by mem_fun()?

Yes - you can use sigc::bind() (see below).

> Actually I want to achieve the effect of
>    sigc::mem_fun(*this, &A::foo)(99);
> but I need to bind 99 to &A::foo, since I need a nullary function
> call.
>
> Below you find an example exhibiting the problem.
>
> Ciao
> Andreas
>
>
> #include <sigc++/sigc++.h>
> #include <boost/bind.hpp>
>
> struct A
> {
>     A()
>     {
> //	sigc::mem_fun(*this, &A::foo)(99);
> 	sigc::mem_fun(*this,
>  		      boost::bind(&A::foo, boost::ref(*this), 99))();

The line above doesn't make sense: the call to sigc::mem_fun() is  
superfluous.
What you want is:

 sigc::bind(sigc::mem_fun(&A::foo, *this), 99)();

or:

 sigc::bind(&A::foo, sigc::ref(*this), 99)();

Note that mixing boost::bind() (and similar stuff) with the sigc API is  
possible but not recommended because auto-disconnection from signals  
that you connect to the resulting functors won't work.

Btw to enable auto-disconnection in your example above, 'A' needs to  
inherit from sigc::trackable:

 struct A : public sigc::trackable
 {
   [...]
 };

 [...]

 some_signal.connect(sigc::mem_fun(&A::foo, A_object));
 // calling some_signal.emit() after A_object got out-of-scope is safe

 [...]

>     }
>
>     void foo(int i){}
> };
>
> int main()
> {
>     A a;
> }

Regards,

 Martin