Re: [Boost-users] [boost::bind] How use with fn objects?

From: BRIDGES Dick (Dick.Bridges_at_[hidden])
Date: 2005-08-29 16:55:13

> -----Original Message-----
> From: boost-users-bounces_at_[hidden] [mailto:boost-users-
> bounces_at_[hidden]] On Behalf Of Rene Rivera
> Sent: Monday, August 29, 2005 12:30 PM
> To: boost-users_at_[hidden]
> Subject: Re: [Boost-users] [boost::bind] How use with fn objects?
> 
> BRIDGES Dick wrote:
[snip]
> > I'm trying to pass a function object that takes no
> > parameters to a boost::thread constructor and cannot
> > get it right.
 [snip]

> Either:
> 
> int
> main( int argc, char **argv ) {
>      Foo f;
>      boost::thread doit( boost:bind(Foo::operator(),&f)() );
>      doit.join();
>      return 0;
> }
> 
> Or:
> 
> int
> main( int argc, char **argv ) {
>      Foo f;
>      boost::thread doit( f );
>      doit.join();
>      return 0;
> }
> 
> Should work.
> 
> 
> --
> -- Grafik - Don't Assume Anything
> -- Redshift Software, Inc. - http://redshift-software.com
> -- rrivera/acm.org - grafik/redshift-software.com
> -- 102708583/icq - grafikrobot/aim - Grafik/jabber.org

After I figured out I had to use boost::ref(f) with my real
class, the second form worked fine.  I had a problem with the
first form though.
<code>
boost::thread doit( boost::bind(Foo::operator(),&f)() );
</code>
Yielded the following [edited to fit] result:
<result>
g++ -D_REENTRANT -I/usr/local -I/usr/local/boost_1_33_0
-I/usr/local/include
  -O0 -g3 -Wall -c -fmessage-length=0 -Wno-non-virtual-dtor -omain.o
../main.cpp
../main.cpp: In function `int main(int, char**)':
../main.cpp:22: error: invalid use of non-static member function
  `void my_namespace::Foo::operator()()'
/usr/local/boost_1_33_0/boost/bind.hpp: At global scope:
/usr/local/boost_1_33_0/boost/bind.hpp: In instantiation of
  `boost::_bi::result_traits<boost::_bi::unspecified, 
  void (my_namespace::Foo::)()>':
/usr/local/boost_1_33_0/boost/bind/bind_template.hpp:15:
  instantiated from `boost::_bi::bind_t<boost::_bi::unspecified,
  void (my_namespace::Foo::)(),
  boost::_bi::list1<boost::_bi::value<my_namespace::Foo*> > >'
../main.cpp:22:   instantiated from here
/usr/local/boost_1_33_0/boost/bind.hpp:63: error:
  `void (my_namespace::Foo::)()' is not a class, struct, or union type
/usr/local/boost_1_33_0/boost/bind/bind_template.hpp: In instantiation
of
  `boost::_bi::bind_t<boost::_bi::unspecified, void
(my_namespace::Foo::)(),
  boost::_bi::list1<boost::_bi::value<my_namespace::Foo*> > >':
../main.cpp:22:   instantiated from here
/usr/local/boost_1_33_0/boost/bind/bind_template.hpp:15: error: no type
  named `type' in `struct
boost::_bi::result_traits<boost::_bi::unspecified,
  void (my_namespace::Foo::)()>'
/usr/local/boost_1_33_0/boost/bind/bind_template.hpp:18: error: no type
  named `type' in `struct
boost::_bi::result_traits<boost::_bi::unspecified,
  void (my_namespace::Foo::)()>'

[snip bind_template.hpp:24 thru bind_template.hpp:138]

/usr/local/boost_1_33_0/boost/bind/bind_template.hpp:143: error: no type
  named `type' in `struct
boost::_bi::result_traits<boost::_bi::unspecified,
  void (my_namespace::Foo::)()>'
/usr/local/boost_1_33_0/boost/bind.hpp: In instantiation of
  `boost::_bi::bind_t<boost::_bi::unspecified, void
(my_namespace::Foo::)(),
  boost::_bi::list1<boost::_bi::value<my_namespace::Foo*> > >':
../main.cpp:22:   instantiated from here
/usr/local/boost_1_33_0/boost/bind/bind_template.hpp:160: error: field
  `boost::_bi::bind_t<boost::_bi::unspecified, void
(my_namespace::Foo::)(),
  boost::_bi::list1<boost::_bi::value<my_namespace::Foo*> > >::f_'
  invalidly declared method type
../main.cpp: In function `int main(int, char**)':
../main.cpp:22: error: no match for call to
  `(boost::_bi::bind_t<boost::_bi::unspecified, void
(my_namespace::Foo::)(),
  boost::_bi::list1<boost::_bi::value<my_namespace::Foo*> > >) ()'
/usr/local/boost_1_33_0/boost/bind.hpp: In constructor
  `boost::_bi::bind_t<R, F, L>::bind_t(F, const L&)
  [with R = boost::_bi::unspecified, F = void (my_namespace::Foo::)(),
  L = boost::_bi::list1<boost::_bi::value<my_namespace::Foo*> >]':
/usr/local/boost_1_33_0/boost/bind.hpp:1403:   instantiated from
  `boost::_bi::bind_t<boost::_bi::unspecified, F,
  typename boost::_bi::list_av_1<A1>::type> boost::bind(F, A1)
  [with F = void (my_namespace::Foo::)(), A1 = my_namespace::Foo*]'
../main.cpp:22:   instantiated from here
/usr/local/boost_1_33_0/boost/bind.hpp:861:
  error: invalid use of non-static member function
make: *** [main.o] Error 1
make: Target `all' not remade because of errors.
</result>

Thank you (and Peter Dimov) for your assistance.

BTW I'm still unclear on *why* (f) works.  It doesn't look like
any pointer to member function I've read about.  Isn't f.operator()
treated like any other member function?  Can someone suggest
something to read that might help me understand?

Thanks again for your help.

Regards,
Dick Bridges