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1 | ;;; -*-lisp-*- |
2 | ;;; | |
dea4d055 | 3 | ;;; Class definitions for main classes |
abdf50aa MW |
4 | ;;; |
5 | ;;; (c) 2009 Straylight/Edgeware | |
6 | ;;; | |
7 | ||
8 | ;;;----- Licensing notice --------------------------------------------------- | |
9 | ;;; | |
e0808c47 | 10 | ;;; This file is part of the Sensible 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 | ||
59146e6e MW |
28 | ;;; Note! You'll notice that none of the classes defined here store property |
29 | ;;; sets persistently, even though there's a `:pset' keyword argument | |
30 | ;;; accepted by many of the classes' initialization methods. That's because | |
31 | ;;; part of the pset protocol involves checking that there are no unused | |
32 | ;;; properties, and this typically happens shortly after the appropriate | |
33 | ;;; objects are constructed. It would be tempting to stash the pset at | |
34 | ;;; initialization time, and then pick some property from it out later -- but | |
35 | ;;; that won't work in general because an error might have been signalled | |
36 | ;;; about that property. It wouldn't surprise me greatly to discover that | |
37 | ;;; `most' code paths resulted in the property being looked up in time to | |
38 | ;;; avoid the unused-property error, but a subtle change in circumstances | |
39 | ;;; then causes a thing done on demand to be done later, leading to | |
40 | ;;; irritating and misleading errors being reported to the user. So please | |
41 | ;;; don't do that. | |
42 | ||
abdf50aa | 43 | ;;;-------------------------------------------------------------------------- |
1f1d88f5 | 44 | ;;; Classes. |
abdf50aa | 45 | |
dea4d055 MW |
46 | (export '(sod-class sod-class-name sod-class-nickname |
47 | sod-class-type sod-class-metaclass | |
48 | sod-class-direct-superclasses sod-class-precedence-list | |
49 | sod-class-chain-link sod-class-chain-head | |
50 | sod-class-chain sod-class-chains | |
a42893dd | 51 | sod-class-slots sod-class-initfrags sod-class-tearfrags |
dea4d055 MW |
52 | sod-class-instance-initializers sod-class-class-initializers |
53 | sod-class-messages sod-class-methods | |
54 | sod-class-state | |
55 | sod-class-ilayout sod-class-vtables)) | |
abdf50aa | 56 | (defclass sod-class () |
77027cca MW |
57 | ((name :initarg :name :type string :reader sod-class-name) |
58 | (location :initarg :location :initform (file-location nil) | |
59 | :type file-location :reader file-location) | |
60 | (nickname :initarg :nick :type string :reader sod-class-nickname) | |
61 | (direct-superclasses :initarg :superclasses :type list | |
abdf50aa | 62 | :reader sod-class-direct-superclasses) |
77027cca | 63 | (chain-link :initarg :link :type (or sod-class null) |
1f1d88f5 | 64 | :reader sod-class-chain-link) |
77027cca | 65 | (metaclass :initarg :metaclass :type sod-class |
abdf50aa | 66 | :reader sod-class-metaclass) |
77027cca MW |
67 | (slots :initarg :slots :initform nil |
68 | :type list :accessor sod-class-slots) | |
69 | (instance-initializers :initarg :instance-initializers :initform nil | |
abdf50aa | 70 | :type list |
abdf50aa | 71 | :accessor sod-class-instance-initializers) |
77027cca MW |
72 | (class-initializers :initarg :class-initializers :initform nil |
73 | :type list :accessor sod-class-class-initializers) | |
b2983f35 MW |
74 | (initargs :initarg :initargs :initform nil |
75 | :type list :accessor sod-class-initargs) | |
a42893dd MW |
76 | (initfrags :initarg :initfrags :initform nil |
77 | :type list :accessor sod-class-initfrags) | |
78 | (tearfrags :initarg :tearfrags :initform nil | |
79 | :type list :accessor sod-class-tearfrags) | |
77027cca MW |
80 | (messages :initarg :messages :initform nil |
81 | :type list :accessor sod-class-messages) | |
82 | (methods :initarg :methods :initform nil | |
83 | :type list :accessor sod-class-methods) | |
abdf50aa | 84 | |
16f9fb72 | 85 | (class-precedence-list :type list :reader sod-class-precedence-list) |
abdf50aa | 86 | |
16f9fb72 | 87 | (%type :type c-class-type :reader sod-class-type) |
ddee4bb1 | 88 | |
16f9fb72 MW |
89 | (chain-head :type sod-class :reader sod-class-chain-head) |
90 | (chain :type list :reader sod-class-chain) | |
91 | (chains :type list :reader sod-class-chains) | |
abdf50aa | 92 | |
16f9fb72 MW |
93 | (%ilayout :type ilayout :reader sod-class-ilayout) |
94 | (effective-methods :type list :reader sod-class-effective-methods) | |
95 | (vtables :type list :reader sod-class-vtables) | |
1f1d88f5 | 96 | |
1645e433 | 97 | (state :initform nil :type (member nil :finalized :broken) |
16f9fb72 | 98 | :reader sod-class-state)) |
abdf50aa MW |
99 | (:documentation |
100 | "Classes describe the layout and behaviour of objects. | |
101 | ||
1f1d88f5 | 102 | The NAME, LOCATION, NICKNAME, DIRECT-SUPERCLASSES, CHAIN-LINK and |
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103 | METACLASS slots are intended to be initialized when the class object is |
104 | constructed: | |
105 | ||
106 | * The NAME is the identifier associated with the class in the user's | |
107 | source file. It is used verbatim in the generated C code as a type | |
108 | name, and must be distinct from other file-scope names in any source | |
109 | file which includes the class definition. Furthermore, other names | |
110 | are derived from the class name (most notably the class object | |
111 | NAME__class), which have external linkage and must therefore be | |
112 | distinct from all other identifiers in the program. It is forbidden | |
113 | for a class NAME to begin with an underscore or to contain two | |
114 | consecutive underscores. | |
115 | ||
116 | * The LOCATION identifies where in the source the class was defined. It | |
117 | gets used in error messages. | |
118 | ||
119 | * The NICKNAME is a shorter identifier used to name the class in some | |
120 | circumstances. The uniqueness requirements on NICKNAME are less | |
121 | strict, which allows them to be shorter: no class may have two classes | |
122 | with the same nickname on its class precedence list. Nicknames are | |
123 | used (user-visibly) to distinguish slots and messages defined by | |
124 | different classes, and (invisibly) in the derived names of direct | |
125 | methods. It is forbidden for a nickname to begin with an underscore, | |
126 | or to contain two consecutive underscores. | |
127 | ||
128 | * The DIRECT-SUPERCLASSES are a list of the class's direct superclasses, | |
129 | in the order that they were declared in the source. The class | |
130 | precedence list is computed from the DIRECT-SUPERCLASSES lists of all | |
131 | of the superclasses involved. | |
132 | ||
1f1d88f5 MW |
133 | * The CHAIN-LINK is either NIL or one of the DIRECT-SUPERCLASSES. Class |
134 | chains are a means for recovering most of the benefits of simple | |
135 | hierarchy lost by the introduction of multiple inheritance. A class's | |
136 | superclasses (including itself) are partitioned into chains, | |
137 | consisting of a class, its CHAIN-LINK superclass, that class's | |
138 | CHAIN-LINK, and so on. It is an error if two direct subclasses of any | |
139 | class appear in the same chain (a global property which requires | |
140 | global knowledge of an entire program's class hierarchy in order to | |
141 | determine sensibly). Slots of superclasses in the same chain can be | |
142 | accessed efficiently; there is an indirection needed to access slots | |
143 | of superclasses in other chains. Furthermore, an indirection is | |
144 | required to perform a cross-chain conversion (i.e., converting a | |
145 | pointer to an instance of some class into a pointer to an instance of | |
146 | one of its superclasses in a different chain), an operation which | |
147 | occurs implicitly in effective methods in order to call direct methods | |
148 | defined on cross-chain superclasses. | |
abdf50aa MW |
149 | |
150 | * The METACLASS is the class of the class object. Classes are objects | |
151 | in their own right, and therefore must be instances of some class; | |
152 | this class is the metaclass. Metaclasses can define additional slots | |
153 | and methods to be provided by their instances; a class definition can | |
154 | provide (C constant expression) initial values for the metaclass | |
155 | instance. | |
156 | ||
157 | The next few slots can't usually be set at object-construction time, since | |
158 | the objects need to contain references to the class object itself. | |
159 | ||
160 | * The SLOTS are a list of the slots defined by the class (instances of | |
dea4d055 | 161 | `sod-slot'). (The class will also define all of the slots defined by |
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162 | its superclasses.) |
163 | ||
164 | * The INSTANCE-INITIALIZERS and CLASS-INITIALIZERS are lists of | |
dea4d055 MW |
165 | initializers for slots (see `sod-initializer' and subclasses), |
166 | providing initial values for instances of the class, and for the | |
167 | class's class object itself, respectively. | |
abdf50aa MW |
168 | |
169 | * The MESSAGES are a list of the messages recognized by the class | |
dea4d055 | 170 | (instances of `sod-message' and subclasses). (Note that the message |
abdf50aa MW |
171 | need not have any methods defined on it. The class will also |
172 | recognize all of the messages defined by its superclasses.) | |
173 | ||
174 | * The METHODS are a list of (direct) methods defined on the class | |
dea4d055 | 175 | (instances of `sod-method' and subclasses). Each method provides |
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176 | behaviour to be invoked by a particular message recognized by the |
177 | class. | |
178 | ||
179 | Other slots are computed from these in order to describe the class's | |
dea4d055 | 180 | layout and effective methods; this is done by `finalize-sod-class'. |
abdf50aa | 181 | |
1f1d88f5 | 182 | * The CLASS-PRECEDENCE-LIST is a list of superclasses in a linear order. |
dea4d055 MW |
183 | It is computed by `compute-class-precedence-list', whose default |
184 | implementation ensures that the order of superclasses is such that (a) | |
185 | subclasses appear before their superclasses; (b) the direct | |
186 | superclasses of a given class appear in the order in which they were | |
187 | declared by the programmer; and (c) classes always appear in the same | |
188 | relative order in all class precedence lists in the same superclass | |
189 | graph. | |
1f1d88f5 MW |
190 | |
191 | * The CHAIN-HEAD is the least-specific class in the class's chain. If | |
192 | there is no link class then the CHAIN-HEAD is the class itself. This | |
193 | slot, like the next two, is computed by the generic function | |
dea4d055 | 194 | `compute-chains'. |
1f1d88f5 MW |
195 | |
196 | * The CHAIN is the list of classes on the complete primary chain, | |
197 | starting from this class and ending with the CHAIN-HEAD. | |
198 | ||
199 | * The CHAINS are the complete collection of chains (most-to-least | |
200 | specific) for the class and all of its superclasses. | |
201 | ||
dea4d055 | 202 | Finally, slots concerning the instance and vtable layout of the class are |
6e6b0958 | 203 | computed on demand (see `define-on-demand-slot'). |
dea4d055 | 204 | |
1f1d88f5 | 205 | * The ILAYOUT describes the layout for an instance of the class. It's |
2aa51854 | 206 | quite complicated; see the documentation of the `ilayout' class for |
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207 | detais. |
208 | ||
209 | * The EFFECTIVE-METHODS are a list of effective methods, specialized for | |
210 | the class. | |
211 | ||
212 | * The VTABLES are a list of descriptions of vtables for the class. The | |
2aa51854 MW |
213 | individual elements are `vtable' objects, which are even more |
214 | complicated than `ilayout' structures. See the class documentation | |
215 | for details.")) | |
abdf50aa MW |
216 | |
217 | (defmethod print-object ((class sod-class) stream) | |
1f1d88f5 MW |
218 | (maybe-print-unreadable-object (class stream :type t) |
219 | (princ (sod-class-name class) stream))) | |
220 | ||
221 | ;;;-------------------------------------------------------------------------- | |
222 | ;;; Slots and initializers. | |
223 | ||
dea4d055 | 224 | (export '(sod-slot sod-slot-name sod-slot-class sod-slot-type)) |
1f1d88f5 | 225 | (defclass sod-slot () |
77027cca MW |
226 | ((name :initarg :name :type string :reader sod-slot-name) |
227 | (location :initarg :location :initform (file-location nil) | |
228 | :type file-location :reader file-location) | |
4b8e5c03 MW |
229 | (%class :initarg :class :type sod-class :reader sod-slot-class) |
230 | (%type :initarg :type :type c-type :reader sod-slot-type)) | |
1f1d88f5 MW |
231 | (:documentation |
232 | "Slots are units of information storage in instances. | |
233 | ||
234 | Each class defines a number of slots, which function similarly to (data) | |
235 | members in structures. An instance contains all of the slots defined in | |
236 | its class and all of its superclasses. | |
237 | ||
238 | A slot carries the following information. | |
239 | ||
240 | * A NAME, which distinguishes it from other slots defined by the same | |
241 | class. Unlike most (all?) other object systems, slots defined in | |
242 | different classes are in distinct namespaces. There are no special | |
243 | restrictions on slot names. | |
244 | ||
245 | * A LOCATION, which states where in the user's source the slot was | |
246 | defined. This gets used in error messages. | |
247 | ||
248 | * A CLASS, which states which class defined the slot. The slot is | |
249 | available in instances of this class and all of its descendents. | |
250 | ||
251 | * A TYPE, which is the C type of the slot. This must be an object type | |
252 | (certainly not a function type, and it must be a complete type by the | |
253 | time that the user header code has been scanned).")) | |
254 | ||
255 | (defmethod print-object ((slot sod-slot) stream) | |
256 | (maybe-print-unreadable-object (slot stream :type t) | |
257 | (pprint-c-type (sod-slot-type slot) stream | |
258 | (format nil "~A.~A" | |
259 | (sod-class-nickname (sod-slot-class slot)) | |
260 | (sod-slot-name slot))))) | |
261 | ||
dea4d055 | 262 | (export '(sod-initializer sod-initializer-slot sod-initializer-class |
a888e3ac | 263 | sod-initializer-value)) |
1f1d88f5 | 264 | (defclass sod-initializer () |
77027cca MW |
265 | ((slot :initarg :slot :type sod-slot :reader sod-initializer-slot) |
266 | (location :initarg :location :initform (file-location nil) | |
267 | :type file-location :reader file-location) | |
4b8e5c03 | 268 | (%class :initarg :class :type sod-class :reader sod-initializer-class) |
a888e3ac | 269 | (value :initarg :value :type c-fragment :reader sod-initializer-value)) |
1f1d88f5 MW |
270 | (:documentation |
271 | "Provides an initial value for a slot. | |
272 | ||
273 | The slots of an initializer are as follows. | |
274 | ||
275 | * The SLOT specifies which slot this initializer is meant to initialize. | |
276 | ||
277 | * The LOCATION states the position in the user's source file where the | |
278 | initializer was found. This gets used in error messages. (Depending | |
279 | on the source layout style, this might differ from the location in the | |
a888e3ac | 280 | VALUE C fragment.) |
1f1d88f5 MW |
281 | |
282 | * The CLASS states which class defined this initializer. For instance | |
dea4d055 MW |
283 | slot initializers (`sod-instance-initializer'), this will be the same |
284 | as the SLOT's class, or be one of its descendants. For class slot | |
285 | initializers (`sod-class-initializer'), this will be an instance of | |
286 | the SLOT's class, or an instance of one of its descendants. | |
1f1d88f5 | 287 | |
a888e3ac | 288 | * The VALUE gives the text of the initializer, as a C fragment. |
1f1d88f5 MW |
289 | |
290 | Typically you'll see instances of subclasses of this class in the wild | |
dea4d055 MW |
291 | rather than instances of this class directly. See `sod-class-initializer' |
292 | and `sod-instance-initializer'.")) | |
1f1d88f5 MW |
293 | |
294 | (defmethod print-object ((initializer sod-initializer) stream) | |
a888e3ac | 295 | (with-slots (slot value) initializer |
882412cf MW |
296 | (if *print-escape* |
297 | (print-unreadable-object (initializer stream :type t) | |
a888e3ac MW |
298 | (format stream "~A = ~A" slot value)) |
299 | (format stream "~A" value)))) | |
1f1d88f5 | 300 | |
dea4d055 | 301 | (export 'sod-class-initializer) |
1f1d88f5 MW |
302 | (defclass sod-class-initializer (sod-initializer) |
303 | () | |
304 | (:documentation | |
305 | "Provides an initial value for a class slot. | |
306 | ||
307 | A class slot initializer provides an initial value for a slot in the class | |
308 | object (i.e., one of the slots defined by the class's metaclass). Its | |
a888e3ac | 309 | VALUE must have the syntax of an initializer, and its consituent |
1f1d88f5 MW |
310 | expressions must be constant expressions. |
311 | ||
dea4d055 | 312 | See `sod-initializer' for more details.")) |
1f1d88f5 | 313 | |
dea4d055 | 314 | (export 'sod-instance-initializer) |
1f1d88f5 MW |
315 | (defclass sod-instance-initializer (sod-initializer) |
316 | () | |
317 | (:documentation | |
318 | "Provides an initial value for a slot in all instances. | |
319 | ||
320 | An instance slot initializer provides an initial value for a slot in | |
a888e3ac MW |
321 | instances of the class. Its VALUE must have the syntax of an initializer. |
322 | Furthermore, if the slot has aggregate type, then you'd better be sure | |
323 | that your compiler supports compound literals (6.5.2.5) because that's | |
324 | what the initializer gets turned into. | |
1f1d88f5 | 325 | |
dea4d055 | 326 | See `sod-initializer' for more details.")) |
1f1d88f5 | 327 | |
b2983f35 MW |
328 | (export 'sod-initarg) |
329 | (defclass sod-initarg () | |
330 | ((%class :initarg :class :type sod-class :reader sod-initarg-class) | |
331 | (location :initarg :location :initform (file-location nil) | |
332 | :type file-location :reader file-location) | |
333 | (name :initarg :name :type string :reader sod-initarg-name) | |
1c1ea17d | 334 | (%type :initarg :type :type c-type :reader sod-initarg-type)) |
b2983f35 MW |
335 | (:documentation |
336 | "Describes a keyword argument accepted by the initialization function.")) | |
337 | ||
338 | (export 'sod-user-initarg) | |
339 | (defclass sod-user-initarg (sod-initarg) | |
340 | ((default :initarg :default :type t :reader sod-initarg-default)) | |
341 | (:documentation | |
342 | "Describes an initialization argument defined by the user.")) | |
343 | ||
344 | (export 'sod-slot-initarg) | |
345 | (defclass sod-slot-initarg (sod-initarg) | |
346 | ((slot :initarg :slot :type sod-slot :reader sod-initarg-slot)) | |
347 | (:documentation | |
348 | "Describes an initialization argument used to initialize a slot.")) | |
349 | ||
1f1d88f5 MW |
350 | ;;;-------------------------------------------------------------------------- |
351 | ;;; Messages and methods. | |
abdf50aa | 352 | |
dea4d055 | 353 | (export '(sod-message sod-message-name sod-message-class sod-message-type)) |
abdf50aa | 354 | (defclass sod-message () |
77027cca MW |
355 | ((name :initarg :name :type string :reader sod-message-name) |
356 | (location :initarg :location :initform (file-location nil) | |
357 | :type file-location :reader file-location) | |
4b8e5c03 MW |
358 | (%class :initarg :class :type sod-class :reader sod-message-class) |
359 | (%type :initarg :type :type c-function-type :reader sod-message-type)) | |
abdf50aa | 360 | (:documentation |
bf090e02 | 361 | "Messages are the means for stimulating an object to behave. |
abdf50aa MW |
362 | |
363 | SOD is a single-dispatch object system, like Smalltalk, C++, Python and so | |
364 | on, but unlike CLOS and Dylan. Behaviour is invoked by `sending messages' | |
365 | to objects. A message carries a name (distinguishing it from other | |
366 | messages recognized by the same class), and a number of arguments; the | |
367 | object may return a value in response. Sending a message therefore looks | |
368 | very much like calling a function; indeed, each message bears the static | |
369 | TYPE signature of a function. | |
370 | ||
371 | An object reacts to being sent a message by executing an `effective | |
372 | method', constructed from the direct methods defined on the recpient's | |
373 | (run-time, not necessarily statically-declared) class and its superclasses | |
374 | according to the message's `method combination'. | |
375 | ||
dea4d055 | 376 | Much interesting work is done by subclasses of `sod-message', which (for |
abdf50aa MW |
377 | example) specify method combinations. |
378 | ||
379 | The slots are as follows. | |
380 | ||
381 | * The NAME distinguishes the message from others defined by the same | |
382 | class. Unlike most (all?) other object systems, messages defined in | |
383 | different classes are in distinct namespaces. It is forbidden for a | |
384 | message name to begin with an underscore, or to contain two | |
385 | consecutive underscores. (Final underscores are fine.) | |
386 | ||
387 | * The LOCATION states where in the user's source the slot was defined. | |
388 | It gets used in error messages. | |
389 | ||
390 | * The CLASS states which class defined the message. | |
391 | ||
392 | * The TYPE is a function type describing the message's arguments and | |
393 | return type. | |
394 | ||
395 | Subclasses can (and probably will) define additional slots.")) | |
396 | ||
1f1d88f5 MW |
397 | (defmethod print-object ((message sod-message) stream) |
398 | (maybe-print-unreadable-object (message stream :type t) | |
399 | (pprint-c-type (sod-message-type message) stream | |
400 | (format nil "~A.~A" | |
401 | (sod-class-nickname (sod-message-class message)) | |
402 | (sod-message-name message))))) | |
403 | ||
dea4d055 MW |
404 | (export '(sod-method sod-method-message sod-method-class sod-method-type |
405 | sod-method-body)) | |
abdf50aa | 406 | (defclass sod-method () |
77027cca MW |
407 | ((message :initarg :message :type sod-message :reader sod-method-message) |
408 | (location :initarg :location :initform (file-location nil) | |
409 | :type file-location :reader file-location) | |
4b8e5c03 MW |
410 | (%class :initarg :class :type sod-class :reader sod-method-class) |
411 | (%type :initarg :type :type c-function-type :reader sod-method-type) | |
77027cca | 412 | (body :initarg :body :type (or c-fragment null) :reader sod-method-body)) |
abdf50aa MW |
413 | (:documentation |
414 | "(Direct) methods are units of behaviour. | |
415 | ||
416 | Methods are the unit of behaviour in SOD. Classes define direct methods | |
417 | for particular messages. | |
418 | ||
419 | When a message is received by an instance, all of the methods defined for | |
420 | that message on that instance's (run-time, not static) class and its | |
421 | superclasses are `applicable'. The applicable methods are gathered | |
422 | together and invoked in some way; the details of this are left to the | |
dea4d055 | 423 | `method combination', determined by the subclass of `sod-message'. |
abdf50aa MW |
424 | |
425 | The slots are as follows. | |
426 | ||
427 | * The MESSAGE describes which meessage invokes the method's behaviour. | |
428 | The method is combined with other methods on the same message | |
429 | according to the message's method combination, to form an `effective | |
430 | method'. | |
431 | ||
432 | * The LOCATION states where, in the user's source, the method was | |
433 | defined. This gets used in error messages. (Depending on the user's | |
434 | coding style, this location might be subtly different from the BODY's | |
435 | location.) | |
436 | ||
437 | * The CLASS specifies which class defined the method. This will be | |
438 | either the class of the message, or one of its descendents. | |
439 | ||
440 | * The TYPE gives the type of the method, including its arguments. This | |
441 | will, in general, differ from the type of the message for several | |
442 | reasons. | |
443 | ||
bf090e02 MW |
444 | -- The method type must include names for all of the method's |
445 | parameters. The message definition can omit the parameter | |
446 | names (in the same way as a function declaration can). Formally, | |
447 | the message definition can contain abstract declarators, whereas | |
448 | method definitions must not. | |
abdf50aa MW |
449 | |
450 | -- Method combinations may require different parameter or return | |
bf090e02 MW |
451 | types. For example, `before' and `after' methods don't |
452 | contribute to the message's return value, so they must be defined | |
453 | as returning `void'. | |
abdf50aa MW |
454 | |
455 | -- Method combinations may permit methods whose parameter and/or | |
bf090e02 MW |
456 | return types don't exactly match the corresponding types of the |
457 | message. For example, one might have methods with covariant | |
458 | return types and contravariant parameter types. (This sounds | |
459 | nice, but it doesn't actually seem like such a clever idea when | |
460 | you consider that the co-/contravariance must hold among all the | |
461 | applicable methods ordered according to the class precedence | |
462 | list. As a result, a user might have to work hard to build | |
463 | subclasses whose CPLs match the restrictions implied by the | |
464 | method types.) | |
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465 | |
466 | Method objects are fairly passive in the SOD translator. However, | |
dea4d055 MW |
467 | subclasses of `sod-message' may (and probably will) construct instances of |
468 | subclasses of `sod-method' in order to carry the additional metadata they | |
abdf50aa MW |
469 | need to keep track of.")) |
470 | ||
1f1d88f5 MW |
471 | (defmethod print-object ((method sod-method) stream) |
472 | (maybe-print-unreadable-object (method stream :type t) | |
473 | (format stream "~A ~@_~A" | |
474 | (sod-method-message method) | |
475 | (sod-method-class method)))) | |
abdf50aa | 476 | |
abdf50aa | 477 | ;;;----- That's all, folks -------------------------------------------------- |