Well that's a lot simpler

README.org

@@ -1,7 +1,7 @@
 * Guile Weak References
 
-This is a simple little library that makes use of the weak hash table functionality in core Guile
-to hackily implement weak references, objects which weakly point to other objects.
+This is a simple little library that makes use of the weak vector functionality in core Guile
+to implement weak references, objects which weakly point to other objects.
 
 The interface is very simple:
 
@@ -12,11 +12,6 @@ The interface is very simple:
 - Get the object associated with the reference, or #f if it has been garbage collected.
 
 ** Implementation
-This is a very simple implementation. There's a globally incremented ID associated with each object, and
-the object is stored in two global weak hash tables, one id-to-object and another object-to-id. The weak
-reference is a record type that stores the ID and also a tombstone property to cache whether the object
-has been collected to avoid the need to look it up after that point.
-
-I created this because I needed an interface outside of the hash tables to refer to single objects instead
-of creating a bunch of weak dictionaries. Also, Guile Hoot does not yet support iteration through weak key
-hash tables, so this will allow me to create a list of weak refs to iterate over instead.
+This is a very simple implementation (thanks David Thompson for a simpler idea). It simply calls a single-
+element weak vector a weak reference. Initially this used the weak hash table support but using a weak
+vector is far simpler and uses less memory.

weakref.scm

@@ -1,40 +1,14 @@
 (define-module (weakref)
-  #:use-module (srfi srfi-9)
-  #:use-module (srfi srfi-9 gnu)
-  #:use-module (srfi srfi-64)
+  #:use-module (ice-9 weak-vector)
   #:export (make-weakref
             weakref?
             weakref-object))
 
-(define *next-id* 0)
-(define *ids-to-objects* (make-weak-value-hash-table))
-(define *objects-to-ids* (make-weak-key-hash-table))
-
-(define-record-type <weakref>
-  (_make-weakref id tombstone)
-  weakref?
-  (id weakref-id)
-  (tombstone weakref-tombstone set-weakref-tombstone!))
-
-(set-record-type-printer!
- <weakref>
- (lambda (ref port)
-   (format port "#<weakref: ~a id=~a>" (or (weakref-object ref) "[gone]") (weakref-id ref))))
+(define (weakref? obj)
+  (and (weak-vector? obj) (= 1 (vector-length obj))))
 
 (define (make-weakref obj)
-  (_make-weakref
-   (or (hashq-ref *objects-to-ids* obj)
-       (let ((id *next-id*))
-         (set! *next-id* (1+ *next-id*))
-         (hashq-set! *ids-to-objects* id obj)
-         (hashq-set! *objects-to-ids* obj id)
-         id))
-   #f))
+  (make-weak-vector 1 obj))
 
 (define (weakref-object ref)
-  (if (weakref-tombstone ref)
-      #f
-      (or (hashq-ref *ids-to-objects* (weakref-id ref))
-          (begin
-            (set-weakref-tombstone! ref #t)
-            #f))))
+  (weak-vector-ref ref 0))