[Boost-users] [boost][lambda] additional placeholders

From: Noel Belcourt (kbelco_at_[hidden])
Date: 2005-11-17 16:34:19

HI,

I'm trying to extend the number of placeholders in boost lambda 1.33.0.  
  There are three available by default and I need at least one more (_4)  
.

I've followed the pattern establish for _3 to define  _4, modifying the  
following files along the way.

// lambda/core.hpp
  boost::lambda::placeholder3_type free3 =  
boost::lambda::placeholder3_type();
  boost::lambda::placeholder4_type free4 =  
boost::lambda::placeholder4_type();

  boost::lambda::placeholder3_type& _3 = free3;
  boost::lambda::placeholder4_type& _4 = free4;

//  lambda/detail/lambda_functors.hpp
template<> struct placeholder<FOURTH> {
   template<class SigArgs> struct sig {
     typedef typename detail::get_element_or_null_type<3, SigArgs>::type  
type;
   };
   template<class RET, CALL_TEMPLATE_ARGS>
   RET call(CALL_FORMAL_ARGS) const { CALL_USE_ARGS; return c; }
};

typedef const lambda_functor<placeholder<THIRD> >  placeholder3_type;
typedef const lambda_functor<placeholder<FOURTH> > placeholder4_type;

// lambda/detail/arity_code.hpp
enum { NONE     = 0x00, // Notice we are using bits as flags here.
        FIRST            = 0x01,
        SECOND      = 0x02,
        THIRD           = 0x04,
        FOURTH       = 0x08,
        EXCEPTION = 0x10,
        RETHROW   = 0x20};

So now _4 is defined but I get compilation errors from  
boost/function/function_template.hpp when I attempt to use _4.  Is  
there some change necessary to either lambda placeholders or to boost  
function to get it to work correctly?

Thanks,

-- Noel Belcourt

// With the changes above, this code fails with the message below.

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

using namespace boost;
using namespace boost::lambda;

typedef function<void (int, int, double, double)> func_t;

template <class T1, class T2, class T3, class T4>
struct A {
   template <class R>
   A(void (R::*required)(T1, T2, T3, T4), R *r) : u(bind(required, r,  
_1, _2, _3, _4)) {}
   func_t u;
};

struct B {
   void f(int, int, double, double);
};

int main(int, char *[])
{
   B b;
   A<int, int, double, double> a(&B::f, &b);
   return 0;
}

This is the error message from CW 9.6 on Darwin

Error   : call of non-function
  (point of instantiation: 'main(int, char **)')
   (instantiating: 'A<int, int, double, double>::A<B>(void (B::*)(int,  
double, double), B *)')
    (instantiating: 'boost::function4<void, int, int, double, double,  
std::allocator<void>>::function4 `base  
constructor'<boost::lambda::lambda_functor<boost::lambda:: 
lambda_functor_base<boost::lambda::action<6,  
boost::lambda::function_action<6, boost::lambda::detail::unspecified>>,  
boost::tuples::tuple<void (B::*const )(int, double, double), B *const ,  
const boost::lambda::lambda_functor<boost::lambda::placeholder<1>>,  
const boost::lambda::lambda_functor<boost::lambda::placeholder<2>>,  
const boost::lambda::lambda_functor<boost::lambda::placeholder<4>>,  
const boost::lambda::lambda_functor<boost::lambda::placeholder<8>>,  
boost::tuples::null_type, boost::tuples::null_type,  
boost::tuples::null_type,  
boost::tuples::null_type>>>>(boost::lambda::lambda_functor<boost:: 
lambda::lambda_functor_base<boost::lambda::action<6,  
boost::lambda::function_action<6, boost::lambda::detail::unspecified>>,  
boost::tuples::tuple<void (B::*const )(int, double, double), B *const ,  
const boost::lambda::lambda_functor<boost::lambda::placeholder<1>>,  
const boost::lambda::lambda_functor<boost::lambda::placeholder<2>>,  
const boost::lambda::lambda_functor<boost::lambda::placeholder<4>>,  
const boost::lambda::lambda_functor<boost::lambda::placeholder<8>>,  
boost::tuples::null_type, boost::tuples::null_type,  
boost::tuples::null_type, boost::tuples::null_type>>>, int)')
     (instantiating: 'boost::function4<void, int, int, double, double,  
std::allocator<void>>::assign_to<boost::lambda::lambda_functor<boost:: 
lambda::lambda_functor_base<boost::lambda::action<6,  
boost::lambda::function_action<6, boost::lambda::detail::unspecified>>,  
boost::tuples::tuple<void (B::*const )(int, double, double), B *const ,  
const boost::lambda::lambda_functor<boost::lambda::placeholder<1>>,  
const boost::lambda::lambda_functor<boost::lambda::placeholder<2>>,  
const boost::lambda::lambda_functor<boost::lambda::placeholder<4>>,  
const boost::lambda::lambda_functor<boost::lambda::placeholder<8>>,  
boost::tuples::null_type, boost::tuples::null_type,  
boost::tuples::null_type,  
boost::tuples::null_type>>>>(boost::lambda::lambda_functor<boost:: 
lambda::lambda_functor_base<boost::lambda::action<6,  
boost::lambda::function_action<6, boost::lambda::detail::unspecified>>,  
boost::tuples::tuple<void (B::*const )(int, double, double), B *const ,  
const boost::lambda::lambda_functor<boost::lambda::placeholder<1>>,  
const boost::lambda::lambda_functor<boost::lambda::placeholder<2>>,  
const boost::lambda::lambda_functor<boost::lambda::placeholder<4>>,  
const boost::lambda::lambda_functor<boost::lambda::placeholder<8>>,  
boost::tuples::null_type, boost::tuples::null_type,  
boost::tuples::null_type, boost::tuples::null_type>>>)')
      (instantiating: 'boost::function4<void, int, int, double, double,  
std::allocator<void>>::assign_to<boost::lambda::lambda_functor<boost:: 
lambda::lambda_functor_base<boost::lambda::action<6,  
boost::lambda::function_action<6, boost::lambda::detail::unspecified>>,  
boost::tuples::tuple<void (B::*const )(int, double, double), B *const ,  
const boost::lambda::lambda_functor<boost::lambda::placeholder<1>>,  
const boost::lambda::lambda_functor<boost::lambda::placeholder<2>>,  
const boost::lambda::lambda_functor<boost::lambda::placeholder<4>>,  
const boost::lambda::lambda_functor<boost::lambda::placeholder<8>>,  
boost::tuples::null_type, boost::tuples::null_type,  
boost::tuples::null_type,  
boost::tuples::null_type>>>>(boost::lambda::lambda_functor<boost:: 
lambda::lambda_functor_base<boost::lambda::action<6,  
boost::lambda::function_action<6, boost::lambda::detail::unspecified>>,  
boost::tuples::tuple<void (B::*const )(int, double, double), B *const ,  
const boost::lambda::lambda_functor<boost::lambda::placeholder<1>>,  
const boost::lambda::lambda_functor<boost::lambda::placeholder<2>>,  
const boost::lambda::lambda_functor<boost::lambda::placeholder<4>>,  
const boost::lambda::lambda_functor<boost::lambda::placeholder<8>>,  
boost::tuples::null_type, boost::tuples::null_type,  
boost::tuples::null_type, boost::tuples::null_type>>>,  
boost::detail::function::function_obj_tag)')
       (instantiating:  
'boost::detail::function::void_function_obj_invoker4<boost::lambda:: 
lambda_functor<boost::lambda::lambda_functor_base<boost::lambda:: 
action<6, boost::lambda::function_action<6,  
boost::lambda::detail::unspecified>>, boost::tuples::tuple<void  
(B::*const )(int, double, double), B *const , const  
boost::lambda::lambda_functor<boost::lambda::placeholder<1>>, const  
boost::lambda::lambda_functor<boost::lambda::placeholder<2>>, const  
boost::lambda::lambda_functor<boost::lambda::placeholder<4>>, const  
boost::lambda::lambda_functor<boost::lambda::placeholder<8>>,  
boost::tuples::null_type, boost::tuples::null_type,  
boost::tuples::null_type, boost::tuples::null_type>>>, void, int, int,  
double, double>::invoke(boost::detail::function::any_pointer, int, int,  
double, double)')
function_template.hpp line 136              
BOOST_FUNCTION_RETURN((*f)(BOOST_FUNCTION_ARGS));

Error   : call of non-function
  (instantiating:  
'boost::detail::function::void_function_obj_invoker4<boost::lambda:: 
lambda_functor<boost::lambda::lambda_functor_base<boost::lambda:: 
action<6, boost::lambda::function_action<6,  
boost::lambda::detail::unspecified>>, boost::tuples::tuple<void  
(B::*const )(int, double, double), B *const , const  
boost::lambda::lambda_functor<boost::lambda::placeholder<1>>, const  
boost::lambda::lambda_functor<boost::lambda::placeholder<2>>, const  
boost::lambda::lambda_functor<boost::lambda::placeholder<4>>, const  
boost::lambda::lambda_functor<boost::lambda::placeholder<8>>,  
boost::tuples::null_type, boost::tuples::null_type,  
boost::tuples::null_type, boost::tuples::null_type>>>, void, int, int,  
double, double>::invoke(boost::detail::function::any_pointer, int, int,  
double, double)')
function_template.hpp line 136              
BOOST_FUNCTION_RETURN((*f)(BOOST_FUNCTION_ARGS));