gcc-you can use this code to learn something about gcc, and inquire further into linux,

				// Build don't link:				#include 								template < class T >				class X				{				  protected:								    union {				        int     x;				        double  y;				    };				};								template < class T >				class Y : public X				{				  public:								    using X::x;								    void        f () { std::cout 				};