Re: guile 3 update, halloween edition

[Andy Wingo <wingo@pobox.com>]

Hey :)

On Thu 31 Oct 2019 15:17, Mikael Djurfeldt <mikael@djurfeldt.com> writes:

> How does the record subtyping relate to GOOPS? I do realize that there
> are issues related to keeping bootstrapping lean, but shouldn't record
> types and classes share mechanisms?

They share the struct layer.

Records are simple: their fields are laid out in order, are all unboxed,
and can be treated as a simple kind of nominal product type.  `match'
takes advantage of this.

GOOPS is more flexible: it can have different slot allocations, unboxed
slots, multiple inheritance, and so on.  Because of multiple inheritance
its accessors have to do dynamic dispatch; whereas for records, if
supertype A allocates slot X to index I, all subtypes will have that
slot in the same place.  A check whether a record is an instance of A is
a simple O(1) check, rather than the CPL search of GOOPS.

Exceptions have a kind of multiple inheritance, but it's more about
object composition than typing.  You can make a compound condition from
a heterogeneous collection of other conditions.  While you could
implement compound conditions with subtyping, it's more straightforward
to use composition.

I think the current status is close to the sweet spot but your thoughts
are welcome :)  I would dearly like to be able to subtype records in
GOOPS, but having looked at it a few times I haven't found quite the
right way to do it.

Cheers,

Andy