repr.cc

// Trivial example of using virtual dispatch to hide template parameters from clients, as
// alluded to here:  http://chapeau.freevariable.com/2009/06/a-problem-of-dependent-types.html

#include <iostream>
#include <list>
#include <tr1/memory>

class repr {
public:
	virtual ~repr() { }
	virtual size_t op() = 0;
};

template <size_t N>
class concrete_repr : public repr {
public:
	virtual ~concrete_repr() { }
	size_t op() {
		return N;
	}
};

typedef std::tr1::shared_ptr<repr> p_repr;
typedef std::list<p_repr> repr_list;
typedef repr_list::iterator repr_it;

int main(int c, char *v[]) {
	repr_list items;
	items.push_back(p_repr(new concrete_repr<2>()));
	items.push_back(p_repr(new concrete_repr<3>()));
	items.push_back(p_repr(new concrete_repr<5>()));
	items.push_back(p_repr(new concrete_repr<7>()));
	items.push_back(p_repr(new concrete_repr<11>()));

	for (repr_it it = items.begin(); it != items.end(); ++it) {
		std::cout << (*it)->op() << std::endl;
	}
}