Adds phantom type (to be used for state/input/output)

lib/phantom.hpp

@@ -0,0 +1,44 @@
+#pragma once
+
+#include <boost/operators.hpp>
+#include <iosfwd>
+
+template <typename Base, typename T>
+struct phantom : boost::operators<phantom<Base, T>>, boost::shiftable<phantom<Base, T>> {
+	phantom(Base y) : x(y) {}
+	explicit operator Base() const { return x; }
+	Base base() const { return x; }
+
+	Base x;
+
+#define IMPL(op)                         \
+	phantom & operator op (phantom rh) { \
+		x op rh.x;                       \
+		return *this;                    \
+	}
+
+	IMPL(+=)
+	IMPL(-=)
+	IMPL(*=)
+	IMPL(/=)
+	IMPL(%=)
+	IMPL(|=)
+	IMPL(&=)
+	IMPL(^=)
+	IMPL(<<=)
+	IMPL(>>=)
+#undef IMPL
+
+	phantom & operator++() { ++x; return *this; }
+	phantom & operator--() { --x; return *this; }
+
+	bool operator<(phantom rh) const { return x < rh.x; }
+	bool operator==(phantom rh) const { return x == rh.x; }
+};
+
+template <typename B, typename T>
+std::ostream & operator<<(std::ostream & out, phantom<B, T> p){ return out << p.x; }
+
+template <typename B, typename T>
+std::istream & operator>>(std::istream & in, phantom<B, T> & p){ return in >> p.x; }
+

src/phantom_test.cpp

@@ -0,0 +1,30 @@
+#include <phantom.hpp>
+#include <iostream>
+
+template <typename T>
+using phantom_int = phantom<int, T>;
+
+struct state_tag;
+using state = phantom_int<state_tag>;
+
+struct input_tag;
+using input = phantom_int<input_tag>;
+
+int main(int argc, char *argv[]){
+	state x = 5;
+	x += 5;
+
+	input y = 9;
+	y -= 9;
+	y++;
+
+	std::cout << (x - 1) << std::endl;
+	std::cout << (y << 1) << std::endl;
+	// std::cout << x+y << std::endl; // does not compile
+
+	for(input i = 0; i < 10; ++i){
+		std::cout << i << ", ";
+	}
+	std::cout << std::endl;
+}
+