[Boost-users] Another lambda question

From: Maximilian Wilson (wilson.max_at_[hidden])
Date: 2004-09-01 13:38:54

I am getting another compiler error when trying to use the lambda
library. Current experiment is string extraction. I'm trying to create
a lambda(x) that pushes any char passed to it onto a particular
string.

      string s2;
      void (std::string::*ft)(char) = &std::string::push_back; 
      // extract function pointer because push_back is overloaded
      char c = 'n';
      bind<void>(ft, var(s2), _1, 1)(c);
            // should push one 'n' onto the string. However, it doesn't compile
      bind<void>(reinterpret_cast<char(std::string::*)(char)>(ft),
var(s2), _1, 1)(c);
            // error messages made me think it might be because
push_back returns void
            // I know this isn't good practice, but I'm just trying to
figure out what's wrong
            // However, this won't compile either.

And then I get this error

/users/user2/ugrad/m/mdw45/boost_1_31_0/boost/lambda/detail/actions.hpp:109:
error: no
   matching function for call to `boost::lambda::function_adaptor<char
   (std::basic_string<char, std::char_traits<char>, std::allocator<char>
   >::*)(char)>::apply(char (std::basic_string<char, std::char_traits<char>,
   std::allocator<char> >::*const&)(char), std::basic_string<char,
   std::char_traits<char>, std::allocator<char> >&, char&, const int&)'

I'm not really sure what the real problem is. Can you tell from
looking at the error message what I should be doing?

Thanks in advance
Max Wilson

(FULL ERROR TEXT FOLLOWS)

/usr/include/boost/lambda/detail/actions.hpp: In static member function `static
   RET boost::lambda::function_action<4, T>::apply(A1&, A2&, A3&, A4&) [with
   RET = void, A1 = char (std::basic_string<char, std::char_traits<char>,
   std::allocator<char> >::*const)(char), A2 = std::basic_string<char,
   std::char_traits<char>, std::allocator<char> >, A3 = char, A4 = const int, T
   = void]':
/usr/include/boost/lambda/detail/lambda_functor_base.hpp:442:  
instantiated from `RET
boost::lambda::lambda_functor_base<boost::lambda::action<4, Act>,
Args>::call(A&, B&, C&, Env&) const [with RET = void, A = char, B =
const boost::tuples::null_type, C = const boost::tuples::null_type,
Env = const boost::tuples::null_type, Act =
boost::lambda::function_action<4, void>, Args =
boost::tuples::tuple<char (std::basic_string<char,
std::char_traits<char>, std::allocator<char> >::*const)(char), const
boost::lambda::lambda_functor<boost::lambda::identity<std::string&> >,
const boost::lambda::lambda_functor<boost::lambda::placeholder<1> >,
const int, boost::tuples::null_type, boost::tuples::null_type,
boost::tuples::null_type, boost::tuples::null_type,
boost::tuples::null_type, boost::tuples::null_type>]'
/usr/include/boost/lambda/detail/lambda_functors.hpp:151:  
instantiated from `typename T::sig<boost::tuples::tuple<A&,
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
boost::lambda::lambda_functor<Base>::operator()(A&) const [with A =
char, T = boost::lambda::lambda_functor_base<boost::lambda::action<4,
boost::lambda::function_action<4, void> >, boost::tuples::tuple<char
(std::basic_string<char, std::char_traits<char>, std::allocator<char>
>::*const)(char), const
boost::lambda::lambda_functor<boost::lambda::identity<std::string&> >,
const boost::lambda::lambda_functor<boost::lambda::placeholder<1> >,
const int, boost::tuples::null_type, boost::tuples::null_type,
boost::tuples::null_type, boost::tuples::null_type,
boost::tuples::null_type, boost::tuples::null_type> >]'
proj1.cpp:180:   instantiated from here
/usr/include/boost/lambda/detail/actions.hpp:109: error: no matching function
   for call to `boost::lambda::function_adaptor<char (std::basic_string<char,
   std::char_traits<char>, std::allocator<char> >::*)(char)>::apply(char
   (std::basic_string<char, std::char_traits<char>, std::allocator<char>
   >::*const&)(char), std::basic_string<char, std::char_traits<char>,
   std::allocator<char> >&, char&, const int&)'
/usr/include/boost/lambda/detail/actions.hpp:109: error: return-statement with
   a value, in function declared with a void return type
bash-2.05b$ g++ proj1.cpp -I /users/user2/ugrad/m/mdw45/boost_1_31_0
/users/user2/ugrad/m/mdw45/boost_1_31_0/boost/lambda/detail/actions.hpp: In
   static member function `static RET boost::lambda::function_action<4,
   T>::apply(A1&, A2&, A3&, A4&) [with RET = void, A1 = char
   (std::basic_string<char, std::char_traits<char>, std::allocator<char>
   >::*const)(char), A2 = std::basic_string<char, std::char_traits<char>,
   std::allocator<char> >, A3 = char, A4 = const int, T = void]':
/users/user2/ugrad/m/mdw45/boost_1_31_0/boost/lambda/detail/lambda_functor_base.hpp:442:
  instantiated from `RET
boost::lambda::lambda_functor_base<boost::lambda::action<4, Act>,
Args>::call(A&, B&, C&, Env&) const [with RET = void, A = char, B =
const boost::tuples::null_type, C = const boost::tuples::null_type,
Env = const boost::tuples::null_type, Act =
boost::lambda::function_action<4, void>, Args =
boost::tuples::tuple<char (std::basic_string<char,
std::char_traits<char>, std::allocator<char> >::*const)(char), const
boost::lambda::lambda_functor<boost::lambda::identity<std::string&> >,
const boost::lambda::lambda_functor<boost::lambda::placeholder<1> >,
const int, boost::tuples::null_type, boost::tuples::null_type,
boost::tuples::null_type, boost::tuples::null_type,
boost::tuples::null_type, boost::tuples::null_type>]'
/users/user2/ugrad/m/mdw45/boost_1_31_0/boost/lambda/detail/lambda_functors.hpp:151:
  instantiated from `typename T::sig<boost::tuples::tuple<A&,
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
boost::lambda::lambda_functor<Base>::operator()(A&) const [with A =
char, T = boost::lambda::lambda_functor_base<boost::lambda::action<4,
boost::lambda::function_action<4, void> >, boost::tuples::tuple<char
(std::basic_string<char, std::char_traits<char>, std::allocator<char>
>::*const)(char), const
boost::lambda::lambda_functor<boost::lambda::identity<std::string&> >,
const boost::lambda::lambda_functor<boost::lambda::placeholder<1> >,
const int, boost::tuples::null_type, boost::tuples::null_type,
boost::tuples::null_type, boost::tuples::null_type,
boost::tuples::null_type, boost::tuples::null_type> >]'
proj1.cpp:180:   instantiated from here
/users/user2/ugrad/m/mdw45/boost_1_31_0/boost/lambda/detail/actions.hpp:109:
error: no
   matching function for call to `boost::lambda::function_adaptor<char
   (std::basic_string<char, std::char_traits<char>, std::allocator<char>
   >::*)(char)>::apply(char (std::basic_string<char, std::char_traits<char>,
   std::allocator<char> >::*const&)(char), std::basic_string<char,
   std::char_traits<char>, std::allocator<char> >&, char&, const int&)'
/users/user2/ugrad/m/mdw45/boost_1_31_0/boost/lambda/detail/actions.hpp:109:
error: return-statement
   with a value, in function declared with a void return type

-- 
Sometimes I think decisions through, weigh the consequences, decide
it is not a good idea, but blind myself and make it anyway. I do not
think this is a good thing to do, but it might be. Humans are
endowed with both reason and emotion for a reason.
   -Tara Greenwood