Well, in Virgil, a class without a superclass is a new root class, with no assumed methods. To use an object of that class as a key in a hashtable, one provides

Well, in Virgil, a class without a superclass is a new root class, with no assumed methods. To use an object of that class as a key in a hashtable, one provides a hash function to the hashtable constructor. (The hash function can be a class method, or a top-level function; with generics, a hashtable key could as well be any type, including primitives). Of course it depends on how your write your code, but most of my objects do not end up as keys in a hashtable, so don't need a hash function nor storage for an identity hashcode. So the smallest object header for a Virgil object is 4 bytes: it's just a type ID that is used for dynamic casts and as an index into a table for GC scanning. Arrays have two 4 byte header fields: the type ID and a 32-bit length. That's considerably more memory efficient than 2 or 3 64-bit header words for Java objects and arrays, respectively.