Unable to use type_traits with Intel Compiler 16 (boost 1.67+)

[nehaljwani]

Source Code:

#include <boost/lexical_cast.hpp>
#include <string>
#include <iostream>

float getSomeNumber()
{
  return 10.0;
}

int main(int argc, char** argv)
{
   std::string mystring("Hello: " + boost::lexical_cast<std::string>(getSomeNumber());
   std::cout << mystring << std::endl;
   return 0;
}

Intel Compiler 16:

 /boost/1.67.0/include/boost/type_traits/is_complete.hpp(45): warning #70: incomplete type is not allowed

       ok_tag<sizeof(T)> check_is_complete(int);
       detected during ....
       ...

/boost/1.67.0/include/boost/type_traits/is_complete.hpp(51): error: template instantiation resulted in unexpected function type of "boost::detail::ok_tag<1U> (int)" (the meaning of a name may have changed since the template declaration -- the type of the template is "boost::detail::ok_tag<sizeof(T)> (int)")
       ...

     detected during: 
        instantiation of "boost::detail::check_is_complete" based on template argument <void> at line 51
        instantiation of class "boost::is_complete<T> [with T=void]" at line 484 of "/Path/to/boost/include/boost/type_traits/is_convertible.hpp"
        ...
        instantiation of "Target boost::lexical_cast<Target, Source>(const Source &) [with Target=std::string, Source=float]" at line 11 of "boostTest.cc"

[nehaljwani]

If this is a compiler bug, could the project please document the list of supported Intel compilers?

[shubhdev]

This seems like a bug in ICC, particularly the expected SFINAE in presence of sizeof(void)doesn't take place which in this case means boost::is_complete<void> breaks.
The below snippet reproduces what's going on. It fails to build on ICC 16, unless the fix is uncommented.

#include <boost/type_traits/is_complete.hpp>
#include <boost/type_traits/integral_constant.hpp>

#include <iostream>

/*
 From https://github.com/boostorg/type_traits/blob/develop/include/boost/type_traits/is_complete.hpp#L53
*/
template <unsigned N>
struct ok_tag { double d; char c[N]; };

template <class T>
ok_tag<sizeof(T)> check_is_complete(int);
template <class T>
char check_is_complete(...);
template <class T> struct is_complete
      : public boost::integral_constant<bool, ::boost::is_function<typename boost::remove_reference<T>::type>::value || (sizeof(boost::detail::check_is_complete<T>(0)) != sizeof(char))> {};
//  FIX
// template <> struct is_complete<void> : public boost::false_type{};
int main(int argc, char** argv)
{
    std::cout << is_complete<void>::value;
   return 0;
}

A fix (hack?) is to specialize the is_complete metafunction for void.