[MIT-Scheme-devel] weak hash table data

[Taylor R Campbell]

Key-weak hash tables are never cleaned automatically, not even in a
secondary GC daemon; unless you call HASH-TABLE/CLEAN! or cause them
to be rehashed, broken entries will retain their data (but not their
keys) strongly.

(let ((a (make-eq-hash-table))
      (b (make-eq-hash-table)))
  (let ((p (list 'p))
        (q (list 'q))
        (r (list 'r)))
    (hash-table/put! a p q)
    (hash-table/put! b q r))
  (gc-flip)
  (list (hash-table/datum-list a)
        (hash-table/datum-list b)))
;Value: (() ((r)))

The manual doesn't claim that *associations* are deleted from weak
hash tables if their keys are reclaimed -- it says only that the hash
table holds its keys weakly --, but this is not the behaviour I expect
for an object called a `weak hash table'.  Does this behaviour worry
anyone else?