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Re: User-defined record types, v2

From: Lars Brinkhoff
Subject: Re: User-defined record types, v2
Date: Sat, 18 Mar 2017 18:13:08 +0100
User-agent: Gnus/5.13 (Gnus v5.13) Emacs/24.3 (gnu/linux)

Update cl-defstruct to use records.

* lisp/emacs-lisp/cl-generic.el (cl--generic-struct-tag): Use type-of.
(cl--generic-struct-specializers): Adjust to new tag.

* lisp/emacs-lisp/cl-macs.el (cl-defstruct): Use type=nil as before.
Use the type symbol as the tag.  Use copy-record to copy structs.
(cl--defstruct-predicate): New function.
(cl--pcase-mutually-exclusive-p): Use it.
(cl-struct-sequence-type): Can now return `record'.

* lisp/emacs-lisp/cl-preloaded.el (cl--make-slot-desc): Adjust ad-hoc
code to new format.
(cl--struct-register-child): Work with records.
(cl-struct-define): Don't touch the tag's symbol-value and
symbol-function slots when we use the type as tag.

diff --git a/lisp/emacs-lisp/cl-generic.el b/lisp/emacs-lisp/cl-generic.el
index 8c6d3d5..e15c942 100644
--- a/lisp/emacs-lisp/cl-generic.el
+++ b/lisp/emacs-lisp/cl-generic.el
@@ -1082,24 +1082,8 @@ cl--generic-eql-used
 ;;; Support for cl-defstructs specializers.
 (defun cl--generic-struct-tag (name &rest _)
-  ;; It's tempting to use (and (vectorp ,name) (aref ,name 0))
-  ;; but that would suffer from some problems:
-  ;; - the vector may have size 0.
-  ;; - when called on an actual vector (rather than an object), we'd
-  ;;   end up returning an arbitrary value, possibly colliding with
-  ;;   other tagcode's values.
-  ;; - it can also result in returning all kinds of irrelevant
-  ;;   values which would end up filling up the method-cache with
-  ;;   lots of irrelevant/redundant entries.
-  ;; FIXME: We could speed this up by introducing a dedicated
-  ;; vector type at the C level, so we could do something like
-  ;; (and (vector-objectp ,name) (aref ,name 0))
-  `(and (vectorp ,name)
-        (> (length ,name) 0)
-        (let ((tag (aref ,name 0)))
-          (and (symbolp tag)
-               (eq (symbol-function tag) :quick-object-witness-check)
-               tag))))
+  ;; Use exactly the same code as for `typeof'.
+  `(if ,name (type-of ,name) 'null))
 (defun cl--generic-class-parents (class)
   (let ((parents ())
@@ -1113,8 +1097,8 @@ cl--generic-class-parents
     (nreverse parents)))
 (defun cl--generic-struct-specializers (tag &rest _)
-  (and (symbolp tag) (boundp tag)
-       (let ((class (symbol-value tag)))
+  (and (symbolp tag)
+       (let ((class (get tag 'cl--class)))
          (when (cl-typep class 'cl-structure-class)
            (cl--generic-class-parents class)))))
diff --git a/lisp/emacs-lisp/cl-macs.el b/lisp/emacs-lisp/cl-macs.el
index 40342f3..7e08ca2 100644
--- a/lisp/emacs-lisp/cl-macs.el
+++ b/lisp/emacs-lisp/cl-macs.el
@@ -2604,11 +2604,24 @@ cl-defstruct
         (print-func nil) (print-auto nil)
         (safety (if (cl--compiling-file) cl--optimize-safety 3))
         (include nil)
-        (tag (intern (format "cl-struct-%s" name)))
+         ;; There are 4 types of structs:
+         ;; - `vector' type: means we should use a vector, which can come
+         ;;   with or without a tag `name', which is usually in slot 0
+         ;;   but obeys :initial-offset.
+         ;; - `list' type: same as `vector' but using lists.
+         ;; - `record' type: means we should use a record, which necessarily
+         ;;   comes tagged in slot 0.  Currently we'll use the `name' as
+         ;;   the tag, but we may want to change it so that the class object
+         ;;   is used as the tag.
+         ;; - nil type: this is the "pre-record default", which uses a vector
+         ;;   with a tag in slot 0 which is a symbol of the form
+         ;;   `cl-struct-NAME'.  We need to still support this for backward
+         ;;   compatibility with old .elc files.
+        (tag name)
         (tag-symbol (intern (format "cl-struct-%s-tags" name)))
         (include-descs nil)
         (include-name nil)
-        (type nil)
+        (type nil)         ;nil here means not specified explicitly.
         (named nil)
         (forms nil)
          (docstring (if (stringp (car descs)) (pop descs)))
@@ -2648,7 +2661,9 @@ cl-defstruct
              ((eq opt :print-function)
               (setq print-func (car args)))
              ((eq opt :type)
-              (setq type (car args)))
+              (setq type (car args))
+               (unless (memq type '(vector list))
+                 (error "Invalid :type specifier: %s" type)))
              ((eq opt :named)
               (setq named t))
              ((eq opt :initial-offset)
@@ -2680,13 +2695,11 @@ cl-defstruct
                    (pop include-descs)))
          (setq descs (append old-descs (delq (assq 'cl-tag-slot descs) descs))
                type inc-type
-               named (if type (assq 'cl-tag-slot descs) 'true))
-         (if (cl--struct-class-named include) (setq tag name named t)))
-      (if type
-         (progn
-           (or (memq type '(vector list))
-               (error "Invalid :type specifier: %s" type))
-           (if named (setq tag name)))
+               named (if (memq type '(vector list))
+                          (assq 'cl-tag-slot descs)
+                        'true))
+         (if (cl--struct-class-named include) (setq named t)))
+      (unless type
        (setq named 'true)))
     (or named (setq descs (delq (assq 'cl-tag-slot descs) descs)))
     (when (and (null predicate) named)
@@ -2696,7 +2709,9 @@ cl-defstruct
                                       (length (memq (assq 'cl-tag-slot descs)
-                            ((memq type '(nil vector))
+                            ((null type) ;Record type.
+                             `(memq (type-of cl-x) ,tag-symbol))
+                            ((eq type 'vector)
                              `(and (vectorp cl-x)
                                    (>= (length cl-x) ,(length descs))
                                    (memq (aref cl-x ,pos) ,tag-symbol)))
@@ -2793,7 +2808,9 @@ cl-defstruct
     (setq slots (nreverse slots)
          defaults (nreverse defaults))
     (and copier
-         (push `(defalias ',copier #'copy-sequence) forms))
+         (push `(defalias ',copier
+                    ,(if (null type) '#'copy-record '#'copy-sequence))
+               forms))
     (if constructor
        (push (list constructor
                     (cons '&key (delq nil (copy-sequence slots))))
@@ -2808,7 +2825,7 @@ cl-defstruct
                     (format "Constructor for objects of type `%s'." name))
                  ,@(if (cl--safe-expr-p `(progn ,@(mapcar #'cl-second descs)))
                        '((declare (side-effect-free t))))
-                 (,(or type #'vector) ,@make))
+                 (,(or type #'record) ,@make))
     (if print-auto (nconc print-func (list '(princ ")" cl-s) t)))
     ;; Don't bother adding to cl-custom-print-functions since it's not used
@@ -2866,6 +2883,15 @@ cl--struct-all-parents
+(defun cl--defstruct-predicate (type)
+  (let ((cons (assq (cl-struct-sequence-type type)
+                    `((list . consp)
+                      (vector . vectorp)
+                      (nil . recordp)))))
+    (if cons
+        (cdr cons)
+      'recordp)))
 (defun cl--pcase-mutually-exclusive-p (orig pred1 pred2)
   "Extra special cases for `cl-typep' predicates."
   (let* ((x1 pred1) (x2 pred2)
@@ -2888,14 +2914,12 @@ cl--pcase-mutually-exclusive-p
                           (memq c2 (cl--struct-all-parents c1)))))))
      (let ((c1 (and (symbolp t1) (cl--find-class t1))))
        (and c1 (cl--struct-class-p c1)
-            (funcall orig (if (eq 'list (cl-struct-sequence-type t1))
-                              'consp 'vectorp)
+            (funcall orig (cl--defstruct-predicate t1)
      (let ((c2 (and (symbolp t2) (cl--find-class t2))))
        (and c2 (cl--struct-class-p c2)
             (funcall orig pred1
-                     (if (eq 'list (cl-struct-sequence-type t2))
-                         'consp 'vectorp))))
+                     (cl--defstruct-predicate t2))))
      (funcall orig pred1 pred2))))
 (advice-add 'pcase--mutually-exclusive-p
             :around #'cl--pcase-mutually-exclusive-p)
@@ -2903,8 +2927,8 @@ cl--pcase-mutually-exclusive-p
 (defun cl-struct-sequence-type (struct-type)
   "Return the sequence used to build STRUCT-TYPE.
-STRUCT-TYPE is a symbol naming a struct type.  Return `vector' or
-`list', or nil if STRUCT-TYPE is not a struct type. "
+STRUCT-TYPE is a symbol naming a struct type.  Return `record',
+`vector`, or `list' if STRUCT-TYPE is a struct type, nil otherwise."
   (declare (side-effect-free t) (pure t))
   (cl--struct-class-type (cl--struct-get-class struct-type)))
diff --git a/lisp/emacs-lisp/cl-preloaded.el b/lisp/emacs-lisp/cl-preloaded.el
index bba7b83..bd77654 100644
--- a/lisp/emacs-lisp/cl-preloaded.el
+++ b/lisp/emacs-lisp/cl-preloaded.el
@@ -64,7 +64,7 @@ cl-struct-cl-structure-object-tags
       ;; cl--slot-descriptor.
       ;; BEWARE: Obviously, it's important to keep the two in sync!
       (lambda (name &optional initform type props)
-        (vector 'cl-struct-cl-slot-descriptor
+        (record 'cl-slot-descriptor
                 name initform type props)))
 (defun cl--struct-get-class (name)
@@ -101,7 +101,7 @@ cl--plist-remove
 (defun cl--struct-register-child (parent tag)
   ;; Can't use (cl-typep parent 'cl-structure-class) at this stage
   ;; because `cl-structure-class' is defined later.
-  (while (vectorp parent)
+  (while (recordp parent)
     (add-to-list (cl--struct-class-children-sym parent) tag)
     ;; Only register ourselves as a child of the leftmost parent since structs
     ;; can only only have one parent.
@@ -150,7 +150,7 @@ cl-struct-define
                    parent name))))
     (add-to-list 'current-load-list `(define-type . ,name))
     (cl--struct-register-child parent-class tag)
-    (unless (eq named t)
+    (unless (or (eq named t) (eq tag name))
       ;; We used to use `defconst' instead of `set' but that
       ;; has a side-effect of purecopying during the dump, so that the
       ;; class object stored in the tag ends up being a *copy* of the

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