Efficient single inheritance

Efficient single inheritance via virtual structs and unification and nesting of structs and enums.
>>Is it possible to provide building blocks in the language, but put inheritance support in the library?

you can already hack internal vtables now with unsafe code,

I liked the idea of adding some safety around that e.g.  a get_vtable<T>(),a 'VTable<T>' intrinsic type, make_vcallable(vtable_ptr,data_ptr) /* with compatibility check the same as for trait objects */  ..  This might be a nice gradual change that would let people handle many cases better , and allow experimenting with unusual things ... a single object with multiple interfaces, using the vtable pointer as state information (a table of event handlers), or "class objects", one vtable associated with a collection of several instances, or 'compressed vtable information' imagine a u8 index to consult an array of known types, if you don't need it completely open.. whatever.