Re: How to get plist properties list?

[Stefan Monnier <monnier@iro.umontreal.ca>]

> (defun mutt-identity-signature (identity)
>   (let* ((sql (format "SELECT * FROM identities WHERE identities_id = %s" identity))
> 	 (list (first (rcd-sql-list sql *cf*)))
> 	 (identity-id (elt list 0))
> 	 (identity-name (elt list 1))
> 	 (identity-first-name (elt list 2))
> 	 (identity-last-name (elt list 3))

That's a completely different situation: the above code does not operate
on a list of elements of arbitrary length, but on what is fundamentally
a tuple of fixed length which just happens to be represented as a Lisp
linked list.

> (defun mapping/map-locations-point-kml-placemark (p)
>   (mapping/kml-placemark (elt p 3) (elt p 4) (list (elt p 0) (elt p 1) (elt p 2))))

Notice that the "n" passed to `elt` is a constant, whereas in the
original code where I pointed out the problem:

    (dotimes (i length (reverse properties))
      (if (divisible-by-2-or-0-p i)
          (push (elt plist i) properties)))))

the argument to `elt` (here `i`) is not a constant.
That changes the nature of the problem completely.

    (elt FOO 100)

may be arguably slow, but it's still constant time, so it won't get
slower when applied to a larger data-structure.  In contrast

    (elt FOO i)

will probably be fairly fast on small data structures, where `i` is
small, but it will get slower and slower as `i` grows with the size of
the data structure.


        Stefan