Stream operators for std::stack

stack-opshift.cc

#include <iostream>
#include <stack>
#include <type_traits>
#include <boost/tti/has_member_function.hpp>

BOOST_TTI_HAS_MEMBER_FUNCTION(push)
BOOST_TTI_HAS_MEMBER_FUNCTION(pop)
BOOST_TTI_HAS_MEMBER_FUNCTION(top)

template <typename C>
constexpr bool has_push() {
	return has_member_function_push<C, void, boost::mpl::vector<typename C::value_type const&>>::value;
}
template <typename C>
constexpr bool has_pop() {
	return has_member_function_pop<C, void>::value;
}
template <typename C>
constexpr bool has_top() {
	return has_member_function_top<C, typename C::reference>::value;
}

template <typename C, typename>
constexpr bool is_possible() {
	return has_push<C>() && has_pop<C>() && has_top<C>();
}

template <typename C, typename U = typename C::value_type>
auto possible() -> typename std::enable_if<is_possible<C,U>(), C>::type;

template <typename C>
auto operator<< (C&& c, typename C::value_type const& v) -> decltype(possible<C>())&& {
	c.push(v);
	return std::move(c);
}
template <typename C>
auto operator<< (C& c, typename C::value_type const& v) -> decltype(possible<C>())& {
	c.push(v);
	return c;
}
template <typename C>
auto operator>> (C&& c, typename C::value_type& v) -> decltype(possible<C>())&& {
	v = c.top();
	c.pop();
	return std::move(c);
}
template <typename C>
auto operator>> (C& c, typename C::value_type& v) -> decltype(possible<C>())& {
	v = c.top();
	c.pop();
	return c;
}
template <typename T> auto COPY(T t) -> T { return t; }

int main(){
	std::stack<int> st;
	st << 1 << 2;
	int a,b;
	auto _t0 = COPY(st) << 3;
	auto _t1 = COPY(st >> a) >> b;
	// force a deref of null so we get into gdb, since gdb's pretty-printer works on std::stack
	*(char volatile*)nullptr = 0;

}