Re: Shouldn't records be sequences?

[Clément Pit-Claudel]

On 12/04/2020 13.23, Stefan Monnier wrote:
>> A recent example: I have a list of records that I display to users,
>> using a custom sort order (a list of record fields).  It's convenient
>> to be able to go from list of fields to list of array offsets once,
>> and then use those offsets in the comparison function (this is similar
>> to what I'd do with C structs).
> 
> Not sure how that relates to treating them as sequences.
> We do want some way to work at the lower level (i.e. access the N'th
> field), which is currently done with `aref` but could be done by
> a `record-ref` instead.

Depends what you mean by sequence, I guess.  I usually think of a sequence as 
anything having an 'nth', so once you have a record-ref that takes an offset 
and returns a value, you might as well call that seq-elt.

> PS: The clean equivalent in Elisp would be to use a list of
> field-accessors instead of a list of fields.  This also saves you from
> converting to a list of array offsets.  But (funcall accessor x) is
> probably significantly slower than (aref x offset), indeed.

That's the exact issue I ran into, yes.
(Well, and the fact that the existence of cl-struct-slot-offset makes it easy 
to get the offset of a field, and I couldn't find a corresponding primitive to 
get an accessor function).
Python solves this issue by having special "accessor" objects that are faster 
to call than the corresponding lambdas ("itemgetter")