C++编译期判断是否能够转型

#include <iostream>
#include <vector>
using namespace std;

template<class T,class U>
class Conversion
{
private:
    typedef char Small;
    class Big{char dummy[2];};
    static Small test(U);
    static Big test(...);
    static T makeT();
public:
    enum{ exists =
        sizeof(test(makeT()))==sizeof(Small) };
    enum{ exists2Way =
        exists && Conversion<U,T>::exists};
    enum{
        sameType=false};
};

template<class T>
class Conversion<T,T>
{
public:
    enum{exists=1,exists2Way=1,sameType=1};
};

#define SUPERSUBCLASS(T,U)
    (Conversion<const U*,const T*>::exists && 
    !Conversion<const T*,const void*>::sameType)
#define SUPERSUBCLASS_STRICT(T,U)
    (SUPERSUBCLASS(T,U) && 
    !Conversion<const T,const U>::sameType)
class Shape
{
public:
    virtual void display()
    {
        cout<<"Shape"<<endl;
    }
};

class Circle:public Shape
{
public:
    virtual void display()
    {
        cout<<"Circle()"<<endl;
    }
};


int _tmain(int argc, _TCHAR* argv[])
{
    cout<<Conversion<double,int>::exists<<endl;
    cout<<SUPERSUBCLASS(Shape,Circle)<<endl;
    cout<<SUPERSUBCLASS_STRICT(Shape,Circle)<<endl;
    return 0;
}