struct and goops questions

[Andy Wingo]

Hi all,

I've been looking at structs a bit recently, and goops' use of them. I
have some questions:

(1) Why are struct free functions part of instances and not vtables? It
would seem that they are more appropriate on the vtables (of course
themselves structs), instead of wasting a word per-instance.

(2) Why are structs double cells? It seems that the last two words are
always zero.

(3) Where does the word "entity" come from? It seems to be a term to
describe invokable objects like procedures-with-setters or generics or
something. Quite confusing, and (it seems) completely undocumented.

(4) What, on a class, are the purpose of slots h0 through h7? They seem
to be unused, and garbage (opaque foo). For example, try doing a
(slot-ref <class> 'h0) a few times -- it makes guile segfault for me.

I bet Mikael knows :)

Thanks,

Andy
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