Quel est le problème avec ce boost :: lambda use?

Question

Pourquoi cette expression boost :: lambda ne fonctionne-t-elle pas?

boost::function<bool (boost::uint64_t, boost::uint64_t&, unsigned int, float)> myFunct = boost::lambda::_3 < 1; 

Je reçois ces erreurs de compilation, cela ne sera probablement pas utile, car elles sont vraiment cryptiques.

|| In file included from /usr/include/boost/function/detail/maybe_include.hpp:33, 
||     from /usr/include/boost/function/detail/function_iterate.hpp:14, 
||     from /usr/include/boost/preprocessor/iteration/detail/iter/forward1.hpp:67, 
||     from /usr/include/boost/function.hpp:64, 
||     from CMoteurRecherche.hpp:13, 
||     from CBenchmark.hpp:4, 
||     from CBenchmark.cpp:1: 
|| /usr/include/boost/function/function_template.hpp: In static member function 'static R boost::detail::function::function_obj_invoker4<FunctionObj, R, T0, T1, T2, T3>::invoke(boost::detail::function::function_buffer&, T0, T1, T2, T3) [with FunctionObj = boost::lambda::lambda_functor<boost::lambda::lambda_functor_base<boost::lambda::explicit_return_type_action<bool>, boost::tuples::tuple<boost::lambda::lambda_functor<boost::lambda::lambda_functor_base<boost::lambda::relational_action<boost::lambda::less_action>, boost::tuples::tuple<boost::lambda::lambda_functor<boost::lambda::placeholder<4> >, 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, 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, boost::tuples::null_type> > >, R = bool, T0 = long unsigned int, T1 = uint64_t&, T2 = unsigned int, T3 = float]': 
/usr/include/boost/function/function_template.hpp|904| instantiated from 'void boost::function4<R, T1, T2, T3, T4>::assign_to(Functor) [with Functor = boost::lambda::lambda_functor<boost::lambda::lambda_functor_base<boost::lambda::explicit_return_type_action<bool>, boost::tuples::tuple<boost::lambda::lambda_functor<boost::lambda::lambda_functor_base<boost::lambda::relational_action<boost::lambda::less_action>, boost::tuples::tuple<boost::lambda::lambda_functor<boost::lambda::placeholder<4> >, 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, 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, boost::tuples::null_type> > >, R = bool, T0 = long unsigned int, T1 = uint64_t&, T2 = uns 
|| igned int, T3 = float]' 
/usr/include/boost/function/function_template.hpp|720| instantiated from 'boost::function4<R, T1, T2, T3, T4>::function4(Functor, typename boost::enable_if_c<boost::type_traits::ice_not::value, int>::type) [with Functor = boost::lambda::lambda_functor<boost::lambda::lambda_functor_base<boost::lambda::explicit_return_type_action<bool>, boost::tuples::tuple<boost::lambda::lambda_functor<boost::lambda::lambda_functor_base<boost::lambda::relational_action<boost::lambda::less_action>, boost::tuples::tuple<boost::lambda::lambda_functor<boost::lambda::placeholder<4> >, 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, 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, boost::tuples::nul 
|| l_type> > >, R = bool, T0 = long unsigned int, T1 = uint64_t&, T2 = unsigned int, T3 = float]' 
/usr/include/boost/function/function_template.hpp|1040| instantiated from 'boost::function<R(T0, T1, T2, T3)>::function(Functor, typename boost::enable_if_c<boost::type_traits::ice_not::value, int>::type) [with Functor = boost::lambda::lambda_functor<boost::lambda::lambda_functor_base<boost::lambda::explicit_return_type_action<bool>, boost::tuples::tuple<boost::lambda::lambda_functor<boost::lambda::lambda_functor_base<boost::lambda::relational_action<boost::lambda::less_action>, boost::tuples::tuple<boost::lambda::lambda_functor<boost::lambda::placeholder<4> >, 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, 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, boost::tuples::null 
|| _type> > >, R = bool, T0 = uint64_t, T1 = uint64_t&, T2 = unsigned int, T3 = float]' 
/usr/include/boost/function/function_template.hpp|1081| instantiated from 'typename boost::enable_if_c<boost::type_traits::ice_not::value, boost::function<R(T0, T1, T2, T3)>&>::type boost::function<R(T0, T1, T2, T3)>::operator=(Functor) [with Functor = boost::lambda::lambda_functor<boost::lambda::lambda_functor_base<boost::lambda::explicit_return_type_action<bool>, boost::tuples::tuple<boost::lambda::lambda_functor<boost::lambda::lambda_functor_base<boost::lambda::relational_action<boost::lambda::less_action>, boost::tuples::tuple<boost::lambda::lambda_functor<boost::lambda::placeholder<4> >, 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, 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, boost::tuples::null_type> > >, R = bool, T0 = uint64_t, T1 = uint64_t&, T2 = unsigned int, T3 = float]' 
/home/mathmoi/MatMoi/CBenchmark.cpp|85| instantiated from here 
/usr/include/boost/function/function_template.hpp|131| error: no match for call to '(boost::lambda::lambda_functor<boost::lambda::lambda_functor_base<boost::lambda::explicit_return_type_action<bool>, boost::tuples::tuple<boost::lambda::lambda_functor<boost::lambda::lambda_functor_base<boost::lambda::relational_action<boost::lambda::less_action>, boost::tuples::tuple<boost::lambda::lambda_functor<boost::lambda::placeholder<4> >, 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, 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, boost::tuples::null_type> > >) (long unsigned int&, long unsigned int&, unsigned int&, float&)' 
/usr/include/boost/lambda/detail/lambda_functors.hpp|137| note: candidates are: typename T::sig<boost::tuples::null_type>::type boost::lambda::lambda_functor<Base>::operator()() const [with T = boost::lambda::lambda_functor_base<boost::lambda::explicit_return_type_action<bool>, boost::tuples::tuple<boost::lambda::lambda_functor<boost::lambda::lambda_functor_base<boost::lambda::relational_action<boost::lambda::less_action>, boost::tuples::tuple<boost::lambda::lambda_functor<boost::lambda::placeholder<4> >, 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, 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, boost::tuples::null_type> >] 

Answer 1

Je pense que la réponse provient de référence Boost.Lambda:

L'utilisation de marqueurs dans l'expression lambda détermine si la fonction résultante est arité, unaire, binaire ou 3-ary . L'indice de substitution le plus élevé est déterminant.

Votre espace réservé le plus élevé est _3, mais la fonction prend 4 arguments. Malheureusement, il semble également d'après la citation, que les espaces réservés ne sont fournis que pour un maximum de 3 arguments.

Par ailleurs, si la fonction a 3 arguments, il semble qu'il serait possible d'utiliser l'opérateur virgule pour montrer l'arité de la fonction (résultat est mis au rebut):

boost::function<bool(int, int, int)> f = boost::lambda::_2 < 1; //error 
boost::function<bool(int, int, int)> f = (boost::lambda::_3, boost::lambda::_2 < 1); //OK