diff -r 7c27cda03747 -r 97df974b5ed5 src/main.h
--- a/src/main.h	Fri Mar 06 23:45:44 2020 +0200
+++ b/src/main.h	Mon Mar 09 14:21:54 2020 +0200
@@ -35,25 +35,65 @@
 
 namespace ldraw
 {
+	class Object;
+
 	// Uniquely identifies a model body object
+	template<typename T>
 	struct Id
 	{
 		std::int32_t value;
-		constexpr bool operator<(ldraw::Id other) const
+		template<typename A, typename B>
+		static constexpr bool is_base_or_base_of = std::disjunction_v<std::is_base_of<A, B>, std::is_base_of<B, A>>;
+		template<typename R, typename = std::enable_if_t<is_base_or_base_of<T, R>>>
+		constexpr bool operator<(ldraw::Id<R> other) const
 		{
 			return this->value < other.value;
 		}
-		friend constexpr unsigned int qHash(ldraw::Id id)
+		friend constexpr unsigned int qHash(ldraw::Id<T> id)
 		{
 			return qHash(id.value);
 		}
-		friend bool operator==(ldraw::Id one, ldraw::Id other)
+		// Allow comparing ids as long as they are related
+		template<typename R, typename = std::enable_if_t<is_base_or_base_of<T, R>>>
+		friend bool operator==(ldraw::Id<T> one, ldraw::Id<R> other)
 		{
 			return one.value == other.value;
 		}
+		// Allow upcasting
+		template<typename R, typename = std::enable_if_t<std::is_base_of_v<R, T>>>
+		constexpr operator Id<R>() const
+		{
+			return Id<R>{this->value};
+		}
 	};
-	using id_t = Id;
-	constexpr id_t NULL_ID = id_t{0};
+
+	using id_t = Id<Object>;
+	using triangleid_t = Id<class Triangle>;
+	using quadrilateralid_t = Id<class Quadrilateral>;
+	using edgeid_t = Id<class EdgeLine>;
+	using conditionaledgeid_t = Id<class ConditionalEdge>;
+	using subfileid_t = Id<class SubfileReference>;
+
+	constexpr struct
+	{
+		template<typename T>
+		constexpr operator Id<T>() const
+		{
+			return Id<T>{0};
+		}
+	} NULL_ID = {};
+
+	template<typename T>
+	inline bool operator==(Id<T> one, decltype(NULL_ID))
+	{
+		return one.value == 0;
+	}
+
+	template<typename T>
+	inline bool operator<(Id<T> one, decltype(NULL_ID))
+	{
+		return one.value < 0;
+	}
 }
 
 constexpr std::size_t operator""_z(const unsigned long long int x)