Шаблонная магия, метафункция IsValidExpression

#include <iostream>

typedef char Small;
class Big {char dummy[2]; };

template <size_t> struct ClassSelector {
    typedef Big type_;
};

template <> struct ClassSelector< sizeof(1)/sizeof(1) > {
    typedef Small type_;
};

#define DECLARE_IS_VALID_EXPRESSION( NAME, U_BASED_RUNTIME_EXPRESSION )\
template< class T > \
struct NAME\
{\
    template< typename U > static typename ClassSelector< sizeof( U_BASED_RUNTIME_EXPRESSION, 1 ) / sizeof( U_BASED_RUNTIME_EXPRESSION, 1 )>::type_ F( void * );\
    template< typename U > static typename ClassSelector<0>::type_ F( ... );\
    enum {  is_valid =  ( sizeof( F<T>( NULL ) ) != sizeof( ClassSelector<0>::type_ ) ) };\
};

struct Foo{ void f(); };
struct Bar{};

DECLARE_IS_VALID_EXPRESSION(HasF,  ( ( U * ) NULL )->f() );

DECLARE_IS_VALID_EXPRESSION(
    IsStreamSerializationSupported,
    ( (std::cout << *(U *)NULL), (std::cin >> *(U *)NULL) ) );

int main(int argc, char *argv[])
{
    std::cout  << HasF<Foo>::is_valid <<
            HasF<Bar>::is_valid <<
            IsStreamSerializationSupported<double>::is_valid <<
            IsStreamSerializationSupported<Bar>::is_valid ;
    return 0;
}