template <typename T>
  struct default_constructible
  {
  private:
    typedef char (&yes)[1];
    typedef char (&no)[2];

    template <unsigned> struct size_type_wrapper { typedef T type; };

    template <class U> static yes check( typename size_type_wrapper<
sizeof( new T ) >::type * );
    template <class U> static no  check( ... );

  public:
    static const bool result =
      sizeof( check<T>(0) ) == sizeof(yes);
  };

  template <bool Val> struct static_assert;
  template <> struct static_assert<true> {};

  struct A { };
  struct B { B(int) {} };

  int main()
  {
    static_assert<  default_constructible< A >::result >();
    static_assert< !default_constructible< B >::result >();
  }

Comeau 4.3 BETA#2 refuses to compile it saying,

"6478.c", line 10: error: no default constructor exists for class "B"
    template <class U> static yes check( typename size_type_wrapper<
sizeof( new U ) >::type * );

Is this correct?  I would have thought that as new B is illegal, sizeof( new
B ) would be, and so typename size_type_wrapper< sizeof( new T ) >::type
ought to be illegal too.

--
Richard Smith