Hi,
The patch below documents the following "issue":
;; What you have in mind is that the `blurps' slot will always refer
;; to a new list.
guile> (define-class <chbouib> ()
(blurps :init-value (list 0)))
guile> (define c (make <chbouib>))
guile> (set-car! (slot-ref c 'blurps) 1)
guile> (slot-ref c 'blurps)
(1)
;; Now, see what happens when a new instance is created...
guile> (define c2 (make <chbouib>))
guile> (set-car! (slot-ref c2 'blurps) 7)
guile> (slot-ref c 'blurps)
(7)
Conclusion: the `init-value' is shared across instance of the class. I
believe this is intentional given that we have `#:init-thunk' to work
around this problem. The patch below is based around this assumption.
Thanks,
Ludovic.
2006-03-01 Ludovic Courtès <[EMAIL PROTECTED]>
* goops.texi (Slot Options): Explain the single-instance pitfall
with `#:init-value' and how to work around it.
--- orig/doc/goops/goops.texi
+++ mod/doc/goops/goops.texi
@@ -833,12 +833,40 @@
@deffnx {slot option} #:init-keyword init-keyword
These options provide various ways to specify how to initialize the
slot's value at instance creation time. @var{init-value} is a fixed
-value. @var{init-thunk} is a procedure of no arguments that is called
-when a new instance is created and should return the desired initial
-slot value. @var{init-form} is an unevaluated expression that gets
+value, @emph{shared across all new instances of the class}.
[EMAIL PROTECTED] is a procedure of no arguments that is called when a
+new instance is created and should return the desired initial slot
+value. @var{init-form} is an unevaluated expression that gets
evaluated when a new instance is created and should return the desired
-initial slot value. @var{init-keyword} is a keyword that can be used to
-pass an initial slot value to @code{make} when creating a new instance.
+initial slot value. @var{init-keyword} is a keyword that can be used
+to pass an initial slot value to @code{make} when creating a new
+instance.
+
+Note that since the @code{init-value} is shared across new instances
+of a class, you may only use it when the initial value is an immutable
+value, like a constant. If you want to initialize a slot with a
+fresh, mutable value, you should use @code{init-thunk} instead to make
+sure that each new instance's slot is initialized with a new object.
+Consider the following example:
+
[EMAIL PROTECTED]
+(define-class <chbouib> ()
+ (hashtab #:init-value (make-hash-table)))
[EMAIL PROTECTED] example
+
+Here, only one hash table is created, and all instances of
[EMAIL PROTECTED]<chbouib>} have their @code{hashtab} slot refer to it. In
order
+to have each instance of @code{<chbouib>} initialized with a new hash
+table, you have to proceed as follow:
+
[EMAIL PROTECTED]
+(define-class <chbouib> ()
+ (hashtab #:init-thunk make-hash-table))
[EMAIL PROTECTED] example
+
+Here, @code{make-hash-table} will be called each time a new instance
+of @code{<chbouib>} is created, thus initializing each @code{hashtab}
+slot with a new hash table.
If more than one of these options is specified for the same slot, the
order of precedence, highest first is
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