Re: How to populate a property list?

[Thien-Thi Nguyen <ttn@glug.org>]

Hattuari <susudata@setidava.kushan.aa> writes:

> a plist has unique keys

only if constructed that way.

consider this *scratch* buffer snapshot:

  (setq x '(:k1 1 :k2 2 :k1 42))
  
  (plist-get x :k1)
  1
  
  (plist-get (cddr x) :k1)
  42

here, `(cddr x)' has unique keys, but `x' does not.  both have the plist
form (i.e., are amenable to passing to `plist-get' or being hung off a
symbol).  if you use `x' w/ assumption of unique keys, certain usage
patterns will end up hiding the second :k1 from you but not actually
recycling it.  result: unsightly (literally!) bloat.  e.g., continuing
from above:

  (setplist 'x x)
  (:k1 1 :k2 2 :k1 42)

  (get 'x :k1)
  1

  (put 'x :k1 "one")
  "one"
  
  (get 'x :k1)
  "one"
  
all's cool from `put' and `get' pov, right?  but the truth is deeper;
ignorance of it does not make it go away:

  x
  (:k1 "one" :k2 2 :k1 42)

thi