-(defun make-std-reader-method-function (class-name slot-name)
- (let* ((pv-table-symbol (gensym))
- (initargs (copy-tree
- (make-method-function
- (lambda (instance)
- (pv-binding1 (.pv. .calls.
- (symbol-value pv-table-symbol)
- (instance) (instance-slots))
- (instance-read-internal
- .pv. instance-slots 1
- (slot-value instance slot-name))))))))
- (setf (getf (getf initargs :plist) :slot-name-lists)
- (list (list nil slot-name)))
- (setf (getf (getf initargs :plist) :pv-table-symbol) pv-table-symbol)
- (list* :method-spec `(reader-method ,class-name ,slot-name)
- initargs)))
+;;;; FINDING SLOT DEFINITIONS
+;;;
+;;; Historical PCL found slot definitions by iterating over
+;;; CLASS-SLOTS, which is O(N) for number of slots, and moreover
+;;; requires a GF call (for SLOT-DEFINITION-NAME) for each slot in
+;;; list up to the desired one.
+;;;
+;;; Current SBCL hashes the effective slot definitions, and some
+;;; information pulled out from them into a simple-vector, with bucket
+;;; chains made out of plists keyed by the slot names. This fixes
+;;; gives O(1) performance, and avoid the GF calls.
+;;;
+;;; MAKE-SLOT-TABLE constructs the hashed vector out of a list of
+;;; effective slot definitions and the class they pertain to, and
+;;; FIND-SLOT-DEFINITION knows how to look up slots in that vector.
+;;;
+;;; The only bit of cleverness in the implementation is to make the
+;;; vectors fairly tight, but always longer then 0 elements:
+;;;
+;;; -- We don't want to waste huge amounts of space no these vectors,
+;;; which are mostly required by things like SLOT-VALUE with a
+;;; variable slot name, so a constant extension over the minimum
+;;; size seems like a good choise.
+;;;
+;;; -- As long as the vector always has a length > 0
+;;; FIND-SLOT-DEFINITION doesn't need to handle the rare case of an
+;;; empty vector separately: it just returns a NIL.
+;;;
+;;; In addition to the slot-definition we also store the slot-location
+;;; and type-check function for instances of standard metaclasses, so
+;;; that SLOT-VALUE &co using variable slot names can get at them
+;;; without additional GF calls.
+;;;
+;;; Notes:
+;;; It would be probably better to store the vector in wrapper
+;;; instead: one less memory indirection, one less CLOS slot
+;;; access to get at it.
+;;;
+;;; It would also be nice to have STANDARD-INSTANCE-STRUCTURE-P
+;;; generic instead of checking versus STANDARD-CLASS and
+;;; FUNCALLABLE-STANDARD-CLASS.
projects / sbcl.git / blobdiff