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Re: User-defined record types

From: Stefan Monnier
Subject: Re: User-defined record types
Date: Wed, 15 Mar 2017 15:12:05 -0400
User-agent: Gnus/5.13 (Gnus v5.13) Emacs/26.0.50 (gnu/linux)

> Thanks.  I got past that and made it through to a dumped emacs which
> uses record types for defstruct by default.


> However, there is still EIEIO which may well need some expert guidance
> to update.

I can take care of that.  Can you put your code on a branch like

>> As mentioned, ideally, we'd want to store the class object directly in
>> the slot 0.  The downside is that prin1 would then dump the class object
>> as well, so when reading dumped objects we'd end up creating another
>> copy of the class object rather than reusing an existing class object.
>> And this will break cl-generic dispatch which compares class objects
>> with `eq`.
> Understood.  I'll look into storing the class object in slot 0.
> I imagine there will be some circular bootstrapping problem, e.g. creating
> the first record object requires a class object which is a record
> object.

Yes, cl-preloaded.el would likely need some extra care to get the system
to bootstrap, but I'm not worried about that.

> Some suggestions:
> - type-of looks into the class object and returns the symbol naming the
>   class.

Yes, that would make a lot of sense, but that means we have to impose
a particular shape on the contents of slot 0.  IOW it means that the
representation of classes is at least somewhat known/imposed by the
C code.  It's probably OK.

> - class-of could be introduced to return a class object, like CLOS.


> - The read/print syntax for records uses the symbol for the type slot.
>   Reading a record would then maybe only work right if the class object
>   has been defined first.  Not sure if that's ok.

Not sure either.  Of course, another option is for prin1 to print the
whole class object in slot 0, and when we read it in, we handle it
specially by looking at the class name inside the class object and
reusing the corresponding class if it already exists.  The would likely
hard-code even more of the notion of class-objects into the C code.


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