Go-like Interfaces in C++

interface.cpp

// Taken from here:
// http://wall.org/~lewis/2012/07/23/go-style-interfaces-in-cpp.html
//
// Some of the code didn't render correctly on the site, here is a full compilable version.

#include <stdlib.h>
#include <stdio.h>

using namespace std;

struct Unknown { };

class Person
{
	// Vtable
	template <class T>
	struct implemented_by
	{
		const char* (T::*name) ();
		void (T::*talk) ();
		static const implemented_by vtable;
	};

	// Interface struct is two pointers long
	const implemented_by<Unknown>* const vt;
	Unknown* const p;

	public:
	// Methods
	inline const char* name () { return (p->*(vt->name))(); }
	inline void talk () { return (p->*(vt->talk))(); }

	// Conversion
	template <class T>
	Person (T* x) : vt(reinterpret_cast<const implemented_by<Unknown> *>
            (&implemented_by<T>::vtable)),
        p(reinterpret_cast<Unknown*>(x))
    { }
};

// Define vtables for all compatible types
template <class T>
const Person::implemented_by<T> Person::implemented_by<T>::vtable = {
    &T::name,
    &T::talk
};

// Person is an interface type with these methods...
//     const char* name ()
//     void talk ()
// This function takes one as an argument
void talkabout (Person t)
{
	printf("%s says:\n", t.name());
	t.talk();
}

// No "implements" declaration, no virtual methods
struct Foo
{
	int x;
	const char* name () { return "Foo"; }
	void talk () { printf("I'm a Foo with a %d!\n", this->x); }
};

// Watch the magic
int main ()
{
	Foo x = {24};
	talkabout(&x);
	return 0;
}