[Boost-users] boost::lambda::bind question

From: Vishnevetsky, Eugene \(IT\) (Eugene.Vishnevetsky_at_[hidden])
Date: 2005-07-01 14:52:35

Is it possible to use boost::ref() or boost::lambda::var() of an
abstract class as a parameter to boost::lambda::bind()?
It seems that compiler attempts to instantiate an object of that
abstract class.
Example:

-----------------
using namespace boost;
using namespace boost::lambda;
class Y
{
public: 
    virtual void foo() = 0;
    void foo2 (){ }
};
class Z : public Y
{
public:
    void foo(){} 
};

class TT
{
public:
    void test( Y& y ) { y.foo2(); }
};

int main()  
{
        std::vector<TT>  xt;
        Z z;    
        Y &y = z; 
        std::for_each (xt.begin(), xt.end(), bind(&TT::test,_1,
ref(y)));
        return 0;
} 
----------------------

And Error message from g++ (GCC) 3.2.3:

---------------------------------
/boost/tuple/detail/tuple_basic.hpp: In instantiation of
`boost::tuples::cons<Y, boost::tuples::null_type>':
/boost/tuple/detail/tuple_basic.hpp:326:   instantiated from
`boost::tuples::cons<boost::tuples::null_type, boost::tuples::cons<Y,
boost::tuples::null_type> >'
/boost/tuple/detail/tuple_basic.hpp:326:   instantiated from
`boost::tuples::cons<void (TT::*const)(Y&),
boost::tuples::cons<boost::tuples::null_type, boost::tuples::cons<Y,
boost::tuples::null_type> > >'
/boost/lambda/detail/lambda_functor_base.hpp:151:   instantiated from
`boost::lambda::detail::has_null_type<boost::tuples::cons<void
(TT::*const)(Y&), boost::tuples::cons<boost::tuples::null_type,
boost::tuples::cons<Y, boost::tuples::null_type> > > >'
/boost/lambda/detail/lambda_functor_base.hpp:229:   instantiated from
`boost::lambda::detail::deduce_non_ref_argument_types<boost::tuples::tup
le<void (TT::*const)(Y&), const
boost::lambda::lambda_functor<boost::lambda::placeholder<1> >, Y&,
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/lambda/detail/lambda_functor_base.hpp:412:   instantiated from
`boost::lambda::lambda_functor_base<boost::lambda::action<3,
boost::lambda::function_action<3, boost::lambda::detail::unspecified> >,
boost::tuples::tuple<void (TT::*const)(Y&), const
boost::lambda::lambda_functor<boost::lambda::placeholder<1> >, Y&,
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::null_type>'
/boost/lambda/detail/lambda_functors.hpp:135:   instantiated from
`boost::lambda::lambda_functor<boost::lambda::lambda_functor_base<boost:
:lambda::action<3, boost::lambda::function_action<3,
boost::lambda::detail::unspecified> >, boost::tuples::tuple<void
(TT::*const)(Y&), const
boost::lambda::lambda_functor<boost::lambda::placeholder<1> >, Y&,
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> > >'
lamtest.cpp:35:   instantiated from here
/boost/tuple/detail/tuple_basic.hpp:320: cannot
declare field `boost::tuples::cons<Y, boost::tuples::null_type>::head'
to be 
of type `Y'
/boost/tuple/detail/tuple_basic.hpp:320: 
because the following virtual functions are abstract:
lamtest.cpp:12:         virtual void Y::foo()
----------------------------------------

Thanks,

Eugene Vishnevetsky
--------------------------------------------------------

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