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1 | ;;; -*-lisp-*- |
2 | ;;; | |
dea4d055 | 3 | ;;; Class finalization implementation |
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4 | ;;; |
5 | ;;; (c) 2009 Straylight/Edgeware | |
6 | ;;; | |
7 | ||
8 | ;;;----- Licensing notice --------------------------------------------------- | |
9 | ;;; | |
dea4d055 | 10 | ;;; This file is part of the Sensble Object Design, an object system for C. |
abdf50aa MW |
11 | ;;; |
12 | ;;; SOD is free software; you can redistribute it and/or modify | |
13 | ;;; it under the terms of the GNU General Public License as published by | |
14 | ;;; the Free Software Foundation; either version 2 of the License, or | |
15 | ;;; (at your option) any later version. | |
16 | ;;; | |
17 | ;;; SOD is distributed in the hope that it will be useful, | |
18 | ;;; but WITHOUT ANY WARRANTY; without even the implied warranty of | |
19 | ;;; MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the | |
20 | ;;; GNU General Public License for more details. | |
21 | ;;; | |
22 | ;;; You should have received a copy of the GNU General Public License | |
23 | ;;; along with SOD; if not, write to the Free Software Foundation, | |
24 | ;;; Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA. | |
25 | ||
26 | (cl:in-package #:sod) | |
27 | ||
28 | ;;;-------------------------------------------------------------------------- | |
dea4d055 | 29 | ;;; Class precedence lists. |
abdf50aa | 30 | |
dea4d055 MW |
31 | ;; Just for fun, we implement a wide selection of precedence list algorithms. |
32 | ;; C3 seems to be clearly the best, with fewer sharp edges for the unwary. | |
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33 | ;; |
34 | ;; The extended precedence graph (EPG) is constructed by adding edges to the | |
35 | ;; superclass graph. If A and B are classes, then write A < B if A is a | |
36 | ;; (maybe indirect) subclass of B. For every two classes A and B, and for | |
37 | ;; every /maximal/ subclass of both A and B (i.e., every C for which C < A | |
38 | ;; and C < B, but there does not exist D such that D < A, D < B and C < D): | |
39 | ;; if A precedes B in C's direct superclass list, then draw an edge A -> B, | |
40 | ;; otherwise draw the edge B -> A. | |
41 | ;; | |
42 | ;; A linearization respects the EPG if, whenever A precedes B in the | |
43 | ;; linearization, there is a path from A to B. The EPG can be cyclic; in | |
44 | ;; that case, we don't care which order the classes in the cycle are | |
45 | ;; linearized. | |
46 | ;; | |
47 | ;; See Barrett, Cassels, Haahr, Moon, Playford, Withington, `A Monotonic | |
48 | ;; Superclass Linearization for Dylan' for more detail. | |
49 | ;; http://www.webcom.com/haahr/dylan/linearization-oopsla96.html | |
50 | ||
dea4d055 MW |
51 | ;;; Tiebreaker functions. |
52 | ||
abdf50aa MW |
53 | (defun clos-tiebreaker (candidates so-far) |
54 | "The CLOS linearization tiebreaker function. | |
55 | ||
bf090e02 MW |
56 | Intended for use with `merge-lists'. Returns the member of CANDIDATES |
57 | which has a direct subclass furthest to the right in the list SO-FAR. | |
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58 | |
59 | This must disambiguate. The SO-FAR list cannot be empty, since the class | |
60 | under construction precedes all of the others. If two classes share a | |
61 | direct subclass then that subclass's direct superclasses list must order | |
62 | them relative to each other." | |
63 | ||
64 | (let (winner) | |
65 | (dolist (class so-far) | |
66 | (dolist (candidate candidates) | |
67 | (when (member candidate (sod-class-direct-superclasses class)) | |
68 | (setf winner candidate)))) | |
69 | (unless winner | |
70 | (error "SOD INTERNAL ERROR: Failed to break tie in CLOS.")) | |
71 | winner)) | |
72 | ||
dea4d055 MW |
73 | (defun c3-tiebreaker (candidates cpls) |
74 | "The C3 linearization tiebreaker function. | |
75 | ||
bf090e02 MW |
76 | Intended for use with `merge-lists'. Returns the member of CANDIDATES |
77 | which appears in the earliest element of CPLS, which should be the list of | |
78 | the class precedence lists of the direct superclasses of the class in | |
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79 | question, in the order specified in the class declaration. |
80 | ||
81 | The only class in the class precedence list which does not appear in one | |
82 | of these lists is the new class itself, which must precede all of the | |
83 | others. | |
84 | ||
85 | This must disambiguate, since if two classes are in the same class | |
86 | precedence list, then one must appear in it before the other, which | |
87 | provides an ordering between them. (In this situation we return the one | |
88 | that matches earliest anyway, which would still give the right answer.) | |
89 | ||
90 | Note that this will merge the CPLs of superclasses /as they are/, not | |
91 | necessarily as C3 would have computed them. This ensures monotonicity | |
92 | assuming that the superclass CPLs are already monotonic. If they aren't, | |
93 | you're going to lose anyway." | |
94 | ||
95 | (dolist (cpl cpls) | |
96 | (dolist (candidate candidates) | |
97 | (when (member candidate cpl) | |
98 | (return-from c3-tiebreaker candidate)))) | |
99 | (error "SOD INTERNAL ERROR: Failed to break tie in C3.")) | |
100 | ||
101 | ;;; Linearization functions. | |
102 | ||
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103 | (defun clos-cpl (class) |
104 | "Compute the class precedence list of CLASS using CLOS linearization rules. | |
105 | ||
106 | We merge the direct-superclass lists of all of CLASS's superclasses, | |
bf090e02 | 107 | disambiguating using `clos-tiebreaker'. |
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108 | |
109 | The CLOS linearization preserves local class ordering, but is not | |
110 | monotonic, and does not respect the extended precedence graph. CLOS | |
111 | linearization will succeed whenever Dylan or C3 linearization succeeds; | |
112 | the converse is not true." | |
113 | ||
114 | (labels ((superclasses (class) | |
115 | (let ((direct-supers (sod-class-direct-superclasses class))) | |
116 | (remove-duplicates (cons class | |
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117 | (mappend #'superclasses |
118 | direct-supers)))))) | |
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119 | (merge-lists (mapcar (lambda (class) |
120 | (cons class | |
121 | (sod-class-direct-superclasses class))) | |
122 | (superclasses class)) | |
123 | :pick #'clos-tiebreaker))) | |
124 | ||
125 | (defun dylan-cpl (class) | |
126 | "Compute the class precedence list of CLASS using Dylan linearization | |
127 | rules. | |
128 | ||
129 | We merge the direct-superclass list of CLASS with the full class | |
130 | precedence lists of its direct superclasses, disambiguating using | |
bf090e02 | 131 | `clos-tiebreaker'. (Inductively, these lists will be consistent with the |
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132 | CPLs of indirect superclasses, since those CPLs' orderings are reflected |
133 | in the CPLs of the direct superclasses.) | |
134 | ||
135 | The Dylan linearization preserves local class ordering and is monotonic, | |
136 | but does not respect the extended precedence graph. | |
137 | ||
138 | Note that this will merge the CPLs of superclasses /as they are/, not | |
139 | necessarily as Dylan would have computed them. This ensures monotonicity | |
140 | assuming that the superclass CPLs are already monotonic. If they aren't, | |
141 | you're going to lose anyway." | |
142 | ||
143 | (let ((direct-supers (sod-class-direct-superclasses class))) | |
144 | (merge-lists (cons (cons class direct-supers) | |
145 | (mapcar #'sod-class-precedence-list direct-supers)) | |
146 | :pick #'clos-tiebreaker))) | |
147 | ||
abdf50aa MW |
148 | (defun c3-cpl (class) |
149 | "Compute the class precedence list of CLASS using C3 linearization rules. | |
150 | ||
151 | We merge the direct-superclass list of CLASS with the full class | |
152 | precedence lists of its direct superclasses, disambiguating using | |
bf090e02 | 153 | `c3-tiebreaker'. |
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154 | |
155 | The C3 linearization preserves local class ordering, is monotonic, and | |
156 | respects the extended precedence graph. It is the linearization used in | |
157 | Python, Perl 6 and other languages. It is the recommended linearization | |
158 | for SOD." | |
159 | ||
160 | (let* ((direct-supers (sod-class-direct-superclasses class)) | |
161 | (cpls (mapcar #'sod-class-precedence-list direct-supers))) | |
162 | (merge-lists (cons (cons class direct-supers) cpls) | |
163 | :pick (lambda (candidates so-far) | |
164 | (declare (ignore so-far)) | |
165 | (c3-tiebreaker candidates cpls))))) | |
166 | ||
167 | (defun flavors-cpl (class) | |
168 | "Compute the class precedence list of CLASS using Flavors linearization | |
169 | rules. | |
170 | ||
171 | We do a depth-first traversal of the superclass graph, ignoring duplicates | |
172 | of classes we've already visited. Interestingly, this has the property of | |
173 | being able to tolerate cyclic superclass graphs, though defining cyclic | |
174 | graphs is syntactically impossible in SOD. | |
175 | ||
176 | This linearization has few other redeeming features, however. In | |
177 | particular, the top class tends not to be at the end of the CPL, despite | |
178 | it being unequivocally less specific than any other class." | |
179 | ||
180 | (let ((done nil)) | |
181 | (labels ((walk (class) | |
182 | (unless (member class done) | |
183 | (push class done) | |
184 | (dolist (super (sod-class-direct-superclasses class)) | |
185 | (walk super))))) | |
186 | (walk class) | |
187 | (nreverse done)))) | |
188 | ||
189 | (defun python-cpl (class) | |
190 | "Compute the class precedence list of CLASS using the documented Python 2.2 | |
191 | linearization rules. | |
192 | ||
193 | We do a depth-first traversal of the superclass graph, retaining only the | |
194 | last occurrence of each class visited. | |
195 | ||
196 | This linearization has few redeeming features. It was never actually | |
197 | implemented; the true Python 2.2 linearization seems closer to (but | |
198 | different from) L*LOOPS." | |
199 | ||
200 | (let ((done nil)) | |
201 | (labels ((walk (class) | |
202 | (push class done) | |
203 | (dolist (super (sod-class-direct-superclasses class)) | |
204 | (walk super)))) | |
205 | (walk class) | |
206 | (delete-duplicates (nreverse done))))) | |
207 | ||
208 | (defun l*loops-cpl (class) | |
209 | "Compute the class precedence list of CLASS using L*LOOPS linearization | |
210 | rules. | |
211 | ||
212 | We merge the class precedence lists of the direct superclasses of CLASS, | |
213 | disambiguating by choosing the earliest candidate which appears in a | |
214 | depth-first walk of the superclass graph. | |
215 | ||
216 | The L*LOOPS rules are monotonic and respect the extended precedence | |
217 | graph. However (unlike Dylan and CLOS) they don't respect local | |
218 | precedence order i.e., the direct-superclasses list orderings." | |
219 | ||
220 | (let ((dfs (flavors-cpl class))) | |
221 | (cons class (merge-lists (mapcar #'sod-class-precedence-list | |
222 | (sod-class-direct-superclasses class)) | |
223 | :pick (lambda (candidates so-far) | |
224 | (declare (ignore so-far)) | |
225 | (dolist (class dfs) | |
226 | (when (member class candidates) | |
227 | (return class)))))))) | |
228 | ||
dea4d055 | 229 | ;;; Default function. |
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230 | |
231 | (defmethod compute-cpl ((class sod-class)) | |
232 | (handler-case (c3-cpl class) | |
233 | (inconsistent-merge-error () | |
234 | (error "Failed to compute class precedence list for `~A'" | |
235 | (sod-class-name class))))) | |
236 | ||
237 | ;;;-------------------------------------------------------------------------- | |
dea4d055 MW |
238 | ;;; Chains. |
239 | ||
240 | (defmethod compute-chains ((class sod-class)) | |
241 | (with-default-error-location (class) | |
242 | (with-slots (chain-link class-precedence-list) class | |
243 | (let* ((head (if chain-link | |
244 | (sod-class-chain-head chain-link) | |
245 | class)) | |
246 | (chain (cons class (and chain-link | |
247 | (sod-class-chain chain-link)))) | |
248 | (table (make-hash-table))) | |
249 | ||
250 | ;; Check the chains. We work through each superclass, maintaining a | |
251 | ;; hash table keyed by class. If we encounter a class C which links | |
252 | ;; to L, then we store C as L's value; if L already has a value then | |
253 | ;; we've found an error. By the end of all of this, the classes | |
254 | ;; which don't have an entry are the chain tails. | |
255 | (dolist (super class-precedence-list) | |
256 | (let ((link (sod-class-chain-link super))) | |
257 | (when link | |
258 | (when (gethash link table) | |
259 | (error "Conflicting chains in class ~A: ~ | |
260 | (~A and ~A both link to ~A)" | |
261 | class super (gethash link table) link)) | |
262 | (setf (gethash link table) super)))) | |
263 | ||
264 | ;; Done. | |
265 | (values head chain | |
266 | (cons chain | |
267 | (mapcar #'sod-class-chain | |
268 | (remove-if (lambda (super) | |
269 | (gethash super table)) | |
270 | (cdr class-precedence-list))))))))) | |
271 | ||
272 | ;;;-------------------------------------------------------------------------- | |
273 | ;;; Sanity checking. | |
274 | ||
275 | (defmethod check-sod-class ((class sod-class)) | |
276 | (with-default-error-location (class) | |
277 | ||
278 | ;; Check the names of things are valid. | |
279 | (with-slots (name nickname messages) class | |
280 | (unless (valid-name-p name) | |
281 | (error "Invalid class name `~A'" class)) | |
282 | (unless (valid-name-p nickname) | |
283 | (error "Invalid class nickname `~A' on class `~A'" nickname class)) | |
284 | (dolist (message messages) | |
285 | (unless (valid-name-p (sod-message-name message)) | |
286 | (error "Invalid message name `~A' on class `~A'" | |
287 | (sod-message-name message) class)))) | |
288 | ||
289 | ;; Check that the slots and messages have distinct names. | |
290 | (with-slots (slots messages class-precedence-list) class | |
291 | (flet ((check-list (list what namefunc) | |
292 | (let ((table (make-hash-table :test #'equal))) | |
293 | (dolist (item list) | |
294 | (let ((name (funcall namefunc item))) | |
295 | (if (gethash name table) | |
296 | (error "Duplicate ~A name `~A' on class `~A'" | |
297 | what name class) | |
298 | (setf (gethash name table) item))))))) | |
299 | (check-list slots "slot" #'sod-slot-name) | |
300 | (check-list messages "message" #'sod-message-name) | |
301 | (check-list class-precedence-list "nickname" #'sod-class-name))) | |
302 | ||
303 | ;; Check that the CHAIN-TO class is actually a proper superclass. (This | |
304 | ;; eliminates hairy things like a class being its own link.) | |
305 | (with-slots (class-precedence-list chain-link) class | |
306 | (unless (or (not chain-link) | |
307 | (member chain-link (cdr class-precedence-list))) | |
308 | (error "In `~A~, chain-to class `~A' is not a proper superclass" | |
309 | class chain-link))) | |
310 | ||
311 | ;; Check for circularity in the superclass graph. Since the superclasses | |
312 | ;; should already be acyclic, it suffices to check that our class is not | |
313 | ;; a superclass of any of its own direct superclasses. | |
314 | (let ((circle (find-if (lambda (super) | |
315 | (sod-subclass-p super class)) | |
316 | (sod-class-direct-superclasses class)))) | |
317 | (when circle | |
318 | (error "Circularity: ~A is already a superclass of ~A" | |
319 | class circle))) | |
320 | ||
321 | ;; Check that the class has a unique root superclass. | |
322 | (find-root-superclass class) | |
323 | ||
324 | ;; Check that the metaclass is a subclass of each direct superclass's | |
325 | ;; metaclass. | |
326 | (with-slots (metaclass direct-superclasses) class | |
327 | (dolist (super direct-superclasses) | |
328 | (unless (sod-subclass-p metaclass (sod-class-metaclass super)) | |
329 | (error "Incompatible metaclass for `~A': ~ | |
330 | `~A' isn't a subclass of `~A' (of `~A')" | |
331 | class metaclass (sod-class-metaclass super) super)))))) | |
332 | ||
333 | ;;;-------------------------------------------------------------------------- | |
334 | ;;; Finalization. | |
335 | ||
336 | (defmethod finalize-sod-class ((class sod-class)) | |
337 | ||
bf090e02 | 338 | ;; CLONE-AND-HACK WARNING: Note that `bootstrap-classes' has a (very brief) |
dea4d055 | 339 | ;; clone of the CPL and chain establishment code. If the interface changes |
bf090e02 | 340 | ;; then `bootstrap-classes' will need to be changed too. |
dea4d055 MW |
341 | |
342 | (with-default-error-location (class) | |
343 | (ecase (sod-class-state class) | |
344 | ((nil) | |
345 | ||
346 | ;; If this fails, mark the class as a loss. | |
347 | (setf (sod-class-state class) :broken) | |
348 | ||
349 | ;; Finalize all of the superclasses. There's some special pleading | |
350 | ;; here to make bootstrapping work: we don't try to finalize the | |
351 | ;; metaclass if we're a root class (no direct superclasses -- because | |
352 | ;; in that case the metaclass will have to be a subclass of us!), or | |
353 | ;; if it's equal to us. This is enough to tie the knot at the top of | |
354 | ;; the class graph. | |
355 | (with-slots (name direct-superclasses metaclass) class | |
356 | (dolist (super direct-superclasses) | |
357 | (finalize-sod-class super)) | |
358 | (unless (or (null direct-superclasses) | |
359 | (eq class metaclass)) | |
360 | (finalize-sod-class metaclass))) | |
361 | ||
362 | ;; Stash the class's type. | |
363 | (setf (sod-class-type class) | |
364 | (make-class-type (sod-class-name class))) | |
365 | ||
366 | ;; Clobber the lists of items if they've not been set. | |
367 | (dolist (slot '(slots instance-initializers class-initializers | |
368 | messages methods)) | |
369 | (unless (slot-boundp class slot) | |
370 | (setf (slot-value class slot) nil))) | |
371 | ||
372 | ;; If the CPL hasn't been done yet, compute it. | |
373 | (with-slots (class-precedence-list) class | |
374 | (unless (slot-boundp class 'class-precedence-list) | |
375 | (setf class-precedence-list (compute-cpl class)))) | |
376 | ||
377 | ;; Check that the class is fairly sane. | |
378 | (check-sod-class class) | |
379 | ||
380 | ;; Determine the class's layout. | |
381 | (with-slots (chain-head chain chains) class | |
382 | (setf (values chain-head chain chains) (compute-chains class))) | |
383 | ||
384 | ;; FIXME: make these slots autovivifying. | |
385 | (with-slots (ilayout effective-methods vtables) class | |
386 | (setf ilayout (compute-ilayout class)) | |
387 | (setf effective-methods (compute-effective-methods class)) | |
388 | (setf vtables (compute-vtables class))) | |
389 | ||
390 | ;; Done. | |
391 | (setf (sod-class-state class) :finalized) | |
392 | t) | |
393 | ||
394 | (:broken | |
395 | nil) | |
396 | ||
397 | (:finalized | |
398 | t)))) | |
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399 | |
400 | ;;;----- That's all, folks -------------------------------------------------- |