Christophe pointed out that the DEFSTRUCT example I posted to the
cmucl-imp mailing list fails in SBCL.:-(
A simpler example of the failure is (DEFUN FOO () (DEFSTRUCT FOO X)).
The problem is that the build-a-constructor code is confidently trying
to find the layout at compile time because it implicitly assumes that
the EVAL-WHEN (COMPILE) stuff setting up the layout got executed already.
And of course when the DEFSTRUCT macro expands in a non-top-level context
this is not correct.
I've made a brute-force patch for this, below, which I'm inclined to
add before 0.7.9, maybe tomorrow. If anyone wants to check to see
whether I've made any new conceptual errors, it'd probably be a good
If performance matters in this case, there is probably some cute way
to use *FORWARD-REFERENCED-LAYOUTS* tricks to make it better, but I
thought the mindlessly straightforward code below was more appropriate
for a last-minute patch.
RCS file: /cvsroot/sbcl/sbcl/src/code/defstruct.lisp,v
retrieving revision 1.46
diff -u -r1.46 defstruct.lisp
--- src/code/defstruct.lisp 17 Oct 2002 19:56:05 -0000 1.46
+++ src/code/defstruct.lisp 23 Oct 2002 12:56:54 -0000
@@ -27,10 +27,36 @@
;;; Delay looking for compiler-layout until the constructor is being
-;;; compiled, since it doesn't exist until after the EVAL-WHEN (COMPILE)
-;;; stuff is compiled.
+;;; compiled, since it doesn't exist until after the EVAL-WHEN
+;;; (COMPILE) stuff is compiled. (Or, in the oddball case when
+;;; DEFSTRUCT is executing in a non-toplevel context, the
+;;; compiler-layout still doesn't exist at compilation time, and we
+;;; delay still further.)
(sb!xc:defmacro %delayed-get-compiler-layout (name)
- `',(compiler-layout-or-lose name))
+ (let ((layout (info :type :compiler-layout name)))
+ (cond (layout
+ ;; ordinary case: When the DEFSTRUCT is at top level,
+ ;; then EVAL-WHEN (COMPILE) stuff will have set up the
+ ;; layout for us to use.
+ (unless (typep (layout-info layout) 'defstruct-description)
+ (error "Class is not a structure class: ~S" name))
+ ;; KLUDGE: In the case that DEFSTRUCT is not at top-level
+ ;; the layout doesn't exist at compile time. In that case
+ ;; we laboriously look it up at run time. This code will
+ ;; run on every constructor call and will likely be quite
+ ;; slow, so if anyone cares about performance of
+ ;; non-toplevel DEFSTRUCTs, it should be rewritten to be
+ ;; cleverer. -- WHN 2002-10-23
+ "implementation limitation: ~
+ Non-toplevel DEFSTRUCT constructors are slow.")
+ (let ((layout (gensym "LAYOUT")))
+ `(let ((,layout (info :type :compiler-layout ',name)))
+ (unless (typep (layout-info ,layout) 'defstruct-description)
+ (error "Class is not a structure class: ~S" ',name))
;;; Get layout right away.
(sb!xc:defmacro compile-time-find-layout (name)
William Harold Newman <william.newman@...>
rather lucky so far
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