[Boost-users] problem with lambda and function<>

From: Arturo_Cuebas_at_[hidden]
Date: 2005-02-18 11:39:44

Given:

#include <map>
#include <boost/mem_fn.hpp>
#include <boost/function.hpp>
#include <boost/lambda/lambda.hpp>
#include <boost/lambda/bind.hpp>

using namespace std;
using namespace boost;
using namespace boost::lambda;

struct s
{
   int key  (){return 1;}
   int value(){return 2;}
};

typedef map<int, int> int_map;
int_map m;
var_type<int_map>::type delayed_m(var(m));

template<class F>
void execute(F f)
{
   s o;
   f(o);
}

Why does this work?:

int main()
{
   execute
   (
      delayed_m[lambda::bind(&s::key,   lambda::_1)] = 
                lambda::bind(&s::value, lambda::_1)
   );
}

But this doesn’t?:

int main()
{
   function<int (s &)> key  (mem_fn(&s::key  )),
                       value(mem_fn(&s::value));

   execute
   (
      delayed_m[key] = value //compile error instantiation backtrace leads 
to here
   );
}

I’m using VC7.1.

Here's the error (sorry that it's so noisy):

c:\Program Files\Microsoft Visual Studio .NET 
2003\Vc7\include\boost\lambda\detail\operator_lambda_func_base.hpp(255) : 
error C2440: '=' : cannot convert from 'const 
boost::tuples::cons<HT,TT>::stored_head_type' to 'int'
        with
        [
            HT=const boost::lambda::detail::parameter_traits_<const 
boost::function<int (s &)>,const boost::lambda::detail::IF<false,const 
boost::function<int (s &)> &,const boost::function<int (s 
&)>>::RET>::type,
 
TT=boost::tuples::detail::map_tuple_to_cons<boost::tuples::null_type,boost::tuples::null_type,boost::tuples::null_type,boost::tuples::null_type,boost::tuples::null_type,boost::tuples::null_type,boost::tuples::null_type,boost::tuples::null_type,boost::tuples::null_type,boost::tuples::null_type>::type
        ]
        No user-defined-conversion operator available that can perform 
this conversion, or the operator cannot be called
        c:\Program Files\Microsoft Visual Studio .NET 
2003\Vc7\include\boost\lambda\detail\lambda_functors.hpp(153) : see 
reference to function template instantiation 'RET 
boost::lambda::lambda_functor_base<Act,Args>::call<boost::lambda::lambda_functor_base<Act,Args>::sig<SigArgs>::type,A,const 
boost::tuples::null_type,const boost::tuples::null_type,const 
boost::tuples::null_type>(A &,B &,C &,Env &) const' being compiled
        with
        [
 
RET=boost::lambda::lambda_functor_base<boost::lambda::other_action<boost::lambda::assignment_action>,boost::tuples::tuple<boost::lambda::lambda_functor<boost::lambda::lambda_functor_base<boost::lambda::other_action<boost::lambda::subscript_action>,boost::tuples::tuple<boost::lambda::lambda_functor<boost::lambda::identity<int_map 
&>>,const boost::lambda::detail::parameter_traits_<const 
boost::function<int (s &)>,const boost::lambda::detail::IF<false,const 
boost::function<int (s &)> &,const boost::function<int (s 
&)>>::RET>::type,boost::tuples::null_type,boost::tuples::null_type,boost::tuples::null_type,boost::tuples::null_type,boost::tuples::null_type,boost::tuples::null_type,boost::tuples::null_type,boost::tuples::null_type>>>,const 
boost::lambda::detail::parameter_traits_<const boost::function<int (s 
&)>,const boost::lambda::detail::IF<false,const boost::function<int (s &)> 
&,const boost::function<int (s 
&)>>::RET>::type,boost::tuples::null_type,boost::tuples::null_type,boost::tuples::null_type,boost::tuples::null_type,boost::tuples::null_type,boost::tuples::null_type,boost::tuples::null_type,boost::tuples::null_type>>::sig<boost::tuples::tuple<s 
&,boost::tuples::null_type,boost::tuples::null_type,boost::tuples::null_type,boost::tuples::null_type,boost::tuples::null_type,boost::tuples::null_type,boost::tuples::null_type,boost::tuples::null_type,boost::tuples::null_type>>::type,
 Act=boost::lambda::other_action<boost::lambda::assignment_action>,
 
Args=boost::tuples::tuple<boost::lambda::lambda_functor<boost::lambda::lambda_functor_base<boos
t::lambda::other_action<boost::lambda::subscript_action>,boost::tuples::tuple<boost::lambda::lambda_functor<boost::lambda::identity<int_map 
&>>,const boost::lambda::detail::parameter_traits_<const 
boost::function<int (s &)>,const boost::lambda::detail::IF<false,const 
boost::function<int (s &)> &,const boost::function<int (s 
&)>>::RET>::type,boost::tuples::null_type,boost::tuples::null_type,boost::tuples::null_type,boost::tuples::null_type,boost::tuples::null_type,boost::tuples::null_type,boost::tuples::null_type,boost::tuples::null_type>>>,const 
boost::lambda::detail::parameter_traits_<const boost::function<int (s 
&)>,const boost::lambda::detail::IF<false,const boost::function<int (s &)> 
&,const boost::function<int (s 
&)>>::RET>::type,boost::tuples::null_type,boost::tuples::null_type,boost::tuples::null_type,boost::tuples::null_type,boost::tuples::null_type,boost::tuples::null_type,boost::tuples::null_type,boost::tuples::null_type>,
            SigArgs=boost::tuples::tuple<s 
&,boost::tuples::null_type,boost::tuples::null_type,boost::tuples::null_type,boost::tuples::null_type,boost::tuples::null_type,boost::tuples::null_type,boost::tuples::null_type,boost::tuples::null_type,boost::tuples::null_type>,
            A=s,
            B=const boost::tuples::null_type,
            C=const boost::tuples::null_type,
            Env=const boost::tuples::null_type
        ]
        c:\TestApps\GeneralTests\GeneralTests.cpp(27) : see reference to 
function template instantiation 
'boost::lambda::lambda_functor_base<Act,Args>::sig<SigArgs>::type 
boost::lambda::lambda_functor<T>::operator ()<s>(A &) const' being 
compiled
        with
        [
 Act=boost::lambda::other_action<boost::lambda::assignment_action>,
 
Args=boost::tuples::tuple<boost::lambda::lambda_functor<boost::lambda::lambda_functor_base<boost::lambda::other_action<boost::lambda::subscript_action>,boost::tuples::tuple<boost::lambda::lambda_functor<boost::lambda::identity<int_map 
&>>,const boost::lambda::detail::parameter_traits_<const 
boost::function<int (s &)>,const boost::lambda::detail::IF<false,const 
boost::function<int (s &)> &,const boost::function<int (s 
&)>>::RET>::type,boost::tuples::null_type,boost::tuples::null_type,boost::tuples::null_type,boost::tuples::null_type,boost::tuples::null_type,boost::tuples::null_type,boost::tuples::null_type,boost::tuples::null_type>>>,const 
boost::lambda::detail::parameter_traits_<const boost::function<int (s 
&)>,const boost::lambda::detail::IF<false,const boost::function<int (s &)> 
&,const boost::function<int (s 
&)>>::RET>::type,boost::tuples::null_type,boost::tuples::null_type,boost::tuples::null_type,boost::tuples::null_type,boost::tuples::null_type,boost::tuples::null_type,boost::tuples::null_type,boost::tuples::null_type>,
            SigArgs=boost::tuples::tuple<s 
&,boost::tuples::null_type,boost::tuples::null_type,boost::tuples::null_type,boost::tuples::null_type,boost::tuples::null_type,boost::tuples::null_type,boost::tuples::null_type,boost::tuples::null_type,boost::tuples::null_type>,
 
T=boost::lambda::lambda_functor_base<boost::lambda::other_action<boost::lambda::assignment_action>,boost::tuples::tuple<boost::lambda::lambda_functor<boost::lambda::lambda_functor_base<boost::lambda::other_action<boost::lambda::subscript_action>,boost::tuples::tuple<boost::lambda::lambda_functor<boost::lambda::identity<int_map 
&>>,const boost::lambda::detail:
:parameter_traits_<const boost::function<int (s &)>,const 
boost::lambda::detail::IF<false,const boost::function<int (s &)> &,const 
boost::function<int (s 
&)>>::RET>::type,boost::tuples::null_type,boost::tuples::null_type,boost::tuples::null_type,boost::tuples::null_type,boost::tuples::null_type,boost::tuples::null_type,boost::tuples::null_type,boost::tuples::null_type>>>,const 
boost::lambda::detail::parameter_traits_<const boost::function<int (s 
&)>,const boost::lambda::detail::IF<false,const boost::function<int (s &)> 
&,const boost::function<int (s 
&)>>::RET>::type,boost::tuples::null_type,boost::tuples::null_type,boost::tuples::null_type,boost::tuples::null_type,boost::tuples::null_type,boost::tuples::null_type,boost::tuples::null_type,boost::tuples::null_type>>,
            A=s
        ]
        c:\TestApps\GeneralTests\GeneralTests.cpp(47) : see reference to 
function template instantiation 'void 
Execute<boost::lambda::lambda_functor<T>>(F)' being compiled
        with
        [
 
T=boost::lambda::lambda_functor_base<boost::lambda::other_action<boost::lambda::assignment_action>,boost::tuples::tuple<boost::lambda::lambda_functor<boost::lambda::lambda_functor_base<boost::lambda::other_action<boost::lambda::subscript_action>,boost::tuples::tuple<boost::lambda::lambda_functor<boost::lambda::identity<int_map 
&>>,const boost::lambda::detail::parameter_traits_<const 
boost::function<int (s &)>,const boost::lambda::detail::IF<false,const 
boost::function<int (s &)> &,const boost::function<int (s 
&)>>::RET>::type,boost::tuples::null_type,boost::tuples::null_type,boost::tuples::null_type,boost::tuples::null_type,boost::tuples::null_type,boost::tuples::null_type,boost::tuples::null_type,boost::tuples::null_type>>>,const 
boost::lambda::detail::parameter_traits_<const boost::function<int (s 
&)>,const boost::lambda::detail::IF<false,const boost::function<int (s &)> 
&,const boost::function<int (s 
&)>>::RET>::type,boost::tuples::null_type,boost::tuples::null_type,boost::tuples::null_type,boost::tuples::null_type,boost::tuples::null_type,boost::tuples::null_type,boost::tuples::null_type,boost::tuples::null_type>>,
 
F=boost::lambda::lambda_functor<boost::lambda::lambda_functor_base<boost::lambda::other_action<boost::lambda::assignment_action>,boost::tuples::tuple<boost::lambda::lambda_functor<boost::lambda::lambda_functor_base<boost::lambda::other_action<boost::lambda::subscript_action>,boost::tuples::tuple<boost::lambda::lambda_functor<boost::lambda::identity<int_map 
&>>,const boost::lambda::detail::parameter_traits_<const 
boost::function<int (s &)>,const boost::lambda::detail::IF<false,const 
boost::function<int (s &)> &,const boost::function<int (s 
&)>>::RET>::type,boost::tuples::null_type,boost::tuples::null_type,boost::tuples::null_type,boost::tuples::null_type,boost::tuples::null_type,boost
::tuples::null_type,boost::tuples::null_type,boost::tuples::null_type>>>,const 
boost::lambda::detail::parameter_traits_<const boost::function<int (s 
&)>,const boost::lambda::detail::IF<false,const boost::function<int (s &)> 
&,const boost::function<int (s 
&)>>::RET>::type,boost::tuples::null_type,boost::tuples::null_type,boost::tuples::null_type,boost::tuples::null_type,boost::tuples::null_type,boost::tuples::null_type,boost::tuples::null_type,boost::tuples::null_type>>>
        ]