fonctionnel, bind1st et mem_fun

Question

Pourquoi ne compilera-t-il pas?

#include <functional> 
#include <boost/function.hpp> 

class A { 
    A() { 
     typedef boost::function<void()> FunctionCall; 
     FunctionCall f = std::bind1st(std::mem_fun(&A::process), this); 
    } 
    void process() {} 
}; 

Erreurs:

In file included from /opt/local/include/gcc44/c++/bits/stl_function.h:712, 
       from /opt/local/include/gcc44/c++/functional:50, 
       from a.cc:1: 
/opt/local/include/gcc44/c++/backward/binders.h: In instantiation of 'std::binder1st<std::mem_fun_t<void, A> >': 
a.cc:7: instantiated from here 
/opt/local/include/gcc44/c++/backward/binders.h:100: error: no type named 'second_argument_type' in 'class std::mem_fun_t<void, A>' 
/opt/local/include/gcc44/c++/backward/binders.h:103: error: no type named 'first_argument_type' in 'class std::mem_fun_t<void, A>' 
/opt/local/include/gcc44/c++/backward/binders.h:106: error: no type named 'first_argument_type' in 'class std::mem_fun_t<void, A>' 
/opt/local/include/gcc44/c++/backward/binders.h:111: error: no type named 'second_argument_type' in 'class std::mem_fun_t<void, A>' 
/opt/local/include/gcc44/c++/backward/binders.h:117: error: no type named 'second_argument_type' in 'class std::mem_fun_t<void, A>' 
/opt/local/include/gcc44/c++/backward/binders.h: In function 'std::binder1st<_Operation> std::bind1st(const _Operation&, const _Tp&) [with _Operation = std::mem_fun_t<void, A>, _Tp = A*]': 
a.cc:7: instantiated from here 
/opt/local/include/gcc44/c++/backward/binders.h:126: error: no type named 'first_argument_type' in 'class std::mem_fun_t<void, A>' 
In file included from /opt/local/include/boost/function/detail/maybe_include.hpp:13, 
       from /opt/local/include/boost/function/detail/function_iterate.hpp:14, 
       from /opt/local/include/boost/preprocessor/iteration/detail/iter/forward1.hpp:47, 
       from /opt/local/include/boost/function.hpp:64, 
       from a.cc:2: 
/opt/local/include/boost/function/function_template.hpp: In static member function 'static void boost::detail::function::void_function_obj_invoker0<FunctionObj, R>::invoke(boost::detail::function::function_buffer&) [with FunctionObj = std::binder1st<std::mem_fun_t<void, A> >, R = void]': 
/opt/local/include/boost/function/function_template.hpp:913: instantiated from 'void boost::function0<R>::assign_to(Functor) [with Functor = std::binder1st<std::mem_fun_t<void, A> >, R = void]' 
/opt/local/include/boost/function/function_template.hpp:722: instantiated from 'boost::function0<R>::function0(Functor, typename boost::enable_if_c<boost::type_traits::ice_not::value, int>::type) [with Functor = std::binder1st<std::mem_fun_t<void, A> >, R = void]' 
/opt/local/include/boost/function/function_template.hpp:1064: instantiated from 'boost::function<R()>::function(Functor, typename boost::enable_if_c<boost::type_traits::ice_not::value, int>::type) [with Functor = std::binder1st<std::mem_fun_t<void, A> >, R = void]' 
a.cc:7: instantiated from here 
/opt/local/include/boost/function/function_template.hpp:153: error: no match for call to '(std::binder1st<std::mem_fun_t<void, A> >)()' 

Answer 1

Parce que bind1st nécessite un objet fonction binaire. Cependant, vous passez un objet fonction unaire. Les classeurs d'objets de fonction de C++ 03 ne sont pas aussi sophistiqués que ceux trouvés dans boost ou tr1. En effet, ils souffrent de problèmes de base comme ne pas pouvoir gérer les fonctions avec des paramètres de référence.

Puisque vous utilisez déjà boost, je vous recommande d'utiliser boost::bind

FunctionCall f = boost::bind(&A::process, this); // yay!