Re: [Boost-users] [type_traits] deduce argument type of member function with function_traits

Subject: Re: [Boost-users] [type_traits] deduce argument type of member function with function_traits
From: alfC (alfredo.correa_at_[hidden])
Date: 2011-09-03 06:26:14

On Saturday, September 3, 2011 1:41:41 AM UTC-7, niXman wrote:
>
> May be: 
> http://www.boost.org/doc/libs/1_47_0/libs/function_types/doc/html/boost_functiontypes/reference/decomposition.html#boost_functiontypes.reference.decomposition.parameter_types
>
> ?
>

good to know! but I still get an error, on this new version.

error: no matching function for call to ‘test(<unresolved overloaded 
function type>)’
/tmp/tt.cpp:25:6: note: candidate is: void test(F) [with F = char 
(csquare_impl::*)(char)const]

but "run" is not overloaded !, and I don't know how to cast to resolve the 
overload.

#include <typeinfo>
#include <iostream>
#include <boost/type_traits/function_traits.hpp>
#include <boost/type_traits/remove_pointer.hpp>
#include <boost/function_types/parameter_types.hpp>
#include <boost/mpl/vector.hpp>
#include <boost/mpl/int.hpp>
#include <boost/mpl/at.hpp>

using namespace std;

double dsquare(double l){ return l*l; }
int isquare(int l){ return l*l; }

struct csquare_impl{
    char run(char c) const{return 'c';}
};
csquare_impl csquare;

template<class F>
void test(F f){
    // works
    // typename boost::function_traits<typename 
boost::remove_pointer<F>::type>::arg1_type test_var;
    // works too, more elegant(?)
    typename boost::mpl::at_c<typename 
boost::function_types::parameter_types<F>::type, 0 >::type test_var;
    cout << typeid(test_var).name() << endl;
}

int main(){
    test(dsquare); // ok, prints "d"(double)
    test(isquare); // ok, prints "i"(int)
    test(csquare.csquare_impl::run);  // not ok, want to print "c"(char)
    return 0;
}

BTW, this type traits is a mess, everything it is all over the place, 
Boost.FunctionTypes, Boost.TypeTraits.FunctionTraits, Boost.Functional.
 

>
> 2011/9/3 alfC <alfredo..._at_[hidden]>
>
>> Is function_traits the right way to extract the argument type of a member 
>> function? 
>>
>> In the following example I want to make the last line work. This will be 
>> part of larger question, on how to deduce the argument type of operator() 
>> for function objects in which operator() is not overloaded.
>>
>> #include <typeinfo>
>> #include <iostream>
>> #include <boost/type_traits/function_traits.hpp>
>> #include <boost/type_traits/remove_pointer.hpp>
>>
>> using namespace std;
>>
>> double dsquare(double l){ return l*l; }
>> int isquare(int l){ return l*l; }
>>
>> struct csquare_impl{
>>     int do(char c) const{
>>         return 'c';
>>     }
>> };
>> csquare_impl csquare;
>>
>> template<class F>
>> void test(F f){
>>     typename boost::function_traits<typename 
>> boost::remove_pointer<F>::type>::arg1_type test_var;
>>     cout << typeid(test_var).name() << endl;
>> }
>>
>> int main(){
>>     test(dsquare); // ok, prints "d"(double)
>>     test(isquare); // ok, prints "i"(int)
>>     test(csquare_impl::do);  // not ok, want to print "c"(char)
>>     return 0;
>> }
>>
>> Thanks,
>> Alfredo
>>
>> _______________________________________________
>> Boost-users mailing list
>> Boost..._at_[hidden]
>> http://lists.boost.org/mailman/listinfo.cgi/boost-users
>>
>
>