Re: [Boost-users] Using bind with function objects

From: Delfin Rojas (drojas_at_[hidden])
Date: 2008-02-28 13:12:46

> Delfin Rojas wrote:

> > Olaf Peter wrote:
> >
> > $ LANG=en g++ bind.cpp -o bind && ./bind
> > /usr/include/boost/bind.hpp: In member function 'R
> > boost::_bi::list2<A1,
> > A2>::operator()(boost::_bi::type<R>, F&, A&, long int) [with R =
int,
> F
> > = Foo, A = boost::_bi::list2<const char*&, const int&>, A1 =
> > boost::arg<1> (*)(), A2 = boost::arg<2> (*)()]':
> > /usr/include/boost/bind/bind_template.hpp:89:   instantiated from
> > 'typename boost::_bi::result_traits<R, F>::type
boost::_bi::bind_t<R,
> > F,
> > L>::operator()(A1&, const A2&) [with A1 = const char*, A2 = int, R =
> > int, F = Foo, L = boost::_bi::list2<boost::arg<1> (*)(),
> boost::arg<2>
> > (*)()>]'
> > bind.cpp:22:   instantiated from here
> > /usr/include/boost/bind.hpp:278: error: void value not ignored as it
> > ought to be
> 
> Foo::operator() is declared void and you are trying to bind it with
> bind<int>. If you change it to bind<void> that error will go away, but
> you will get another error about not being able to convert int into
> int&. I believe this because of the forwarding problem (see the boost
> bind documentation under "Limitations"). So, in order to make it work
> you need:
> 
> struct Bar {
> 
>     Bar( Foo& foo_ ) : foo( foo_ ) { }
> 
>     void operator()( const char* s_ ) {
>         bind<void>(foo, _1, 42)(s_);
>     }
> 
>     Foo& foo;
> };
> 
> Hope this helps,

Sorry, I meant:

struct Bar {

    Bar( Foo& foo_ ) : foo( foo_ ) { }

    void operator()( const char* s_ ) {
        bind<void>(foo, _1, 42)(s_);
    }

    Foo& foo;
};

That compiles for me in VC++ 8

-delfin