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

From: Roman Krylov (Roman.Krylov_at_[hidden])
Date: 2005-07-04 09:29:14

Perhaps the only solution here is to use Y* instead of Y& with 
corresponding modifications; this way there is no need for var() or smth 
similar. Why not?

Vishnevetsky, Eugene (IT) wrote:

>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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>
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