Testing <type_traits>

[Jonathan Wakely]

Most type traits have a requirements/typedefs.cc test like this:

#include <type_traits>

void test01()
{
  // Check for required typedefs
  typedef std::has_virtual_destructor<int>	test_type;
  typedef test_type::value_type			value_type;
  typedef test_type::type			type;
  typedef test_type::type::value_type		type_value_type;
  typedef test_type::type::type			type_type;
}

Wouldn't it be better to do something like this instead?

  typedef std::has_virtual_destructor<int>       test_type;
  static_assert( std::is_same<test_type::value_type, bool>::value, "" );
  typedef integral_constant<bool, test_type()()> bool_type;
  static_assert( std::is_same<test_type::type, bool_type>::value, "");

We should be checking that ::type is bool_constant, and if we do that
then we don't need to bother testing type::type and type::value_type.