c++ - 功能性、bind1st 和 mem_fun

Question

为什么不能编译？

#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() {} 
};

错误:

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

因为 bind1st 需要一个二元函数对象。但是，您传递了一个一元函数对象。 C++03 的函数对象绑定(bind)器不像 boost 或 tr1 中的那样复杂。事实上，它们存在一些基本问题，比如无法处理带有引用参数的函数。

既然你已经使用了boost，我推荐使用boost::bind

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