/interpreter/tags/at2dist170907/src/edu/vub/at/objects/ATObject.java
Java | 967 lines | 67 code | 57 blank | 843 comment | 0 complexity | 330b16a5f6e137a46e0eeeb390908c2e MD5 | raw file
1/** 2 * AmbientTalk/2 Project 3 * ATObject.java created on 13-jul-2006 at 15:33:42 4 * (c) Programming Technology Lab, 2006 - 2007 5 * Authors: Tom Van Cutsem & Stijn Mostinckx 6 * 7 * Permission is hereby granted, free of charge, to any person 8 * obtaining a copy of this software and associated documentation 9 * files (the "Software"), to deal in the Software without 10 * restriction, including without limitation the rights to use, 11 * copy, modify, merge, publish, distribute, sublicense, and/or 12 * sell copies of the Software, and to permit persons to whom the 13 * Software is furnished to do so, subject to the following 14 * conditions: 15 * 16 * The above copyright notice and this permission notice shall be 17 * included in all copies or substantial portions of the Software. 18 * 19 * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, 20 * EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES 21 * OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND 22 * NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT 23 * HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, 24 * WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING 25 * FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR 26 * OTHER DEALINGS IN THE SOFTWARE. 27 */ 28package edu.vub.at.objects; 29 30import edu.vub.at.actors.ATAsyncMessage; 31import edu.vub.at.exceptions.InterpreterException; 32import edu.vub.at.exceptions.XArityMismatch; 33import edu.vub.at.exceptions.XDuplicateSlot; 34import edu.vub.at.exceptions.XIllegalQuote; 35import edu.vub.at.exceptions.XIllegalUnquote; 36import edu.vub.at.exceptions.XObjectOffline; 37import edu.vub.at.exceptions.XSelectorNotFound; 38import edu.vub.at.exceptions.XUnassignableField; 39import edu.vub.at.exceptions.XUndefinedSlot; 40import edu.vub.at.objects.coercion.ATConversions; 41import edu.vub.at.objects.grammar.ATAssignmentSymbol; 42import edu.vub.at.objects.grammar.ATSymbol; 43import edu.vub.at.objects.mirrors.NATMirage; 44import edu.vub.at.objects.mirrors.OBJMirrorRoot; 45import edu.vub.at.objects.natives.NATCallframe; 46import edu.vub.at.objects.natives.NATObject; 47import edu.vub.at.objects.natives.NATText; 48import edu.vub.at.objects.natives.NativeATObject; 49import edu.vub.at.objects.symbiosis.JavaClass; 50import edu.vub.at.objects.symbiosis.JavaObject; 51 52/** 53 * ATObject represents the public interface common to any AmbientTalk/2 object. 54 * Any value representing an ambienttalk object should implement this interface. 55 * 56 * More specifically, this interface actually defines two interfaces all at once: 57 * <ul> 58 * <li>A <b>base-level</b> interface to AmbientTalk objects, describing all 59 * methods and fields that a regular AmbientTalk object understands. 60 * <li>A <b>meta-level</b> interface to AmbientTalk objects, describing all 61 * methods and fields that the <b>mirror</b> on any AmbientTalk object 62 * understands. 63 * </ul> 64 * 65 * In the AmbientTalk/2 Interpreter implementation, there are only a few classes 66 * that (almost) fully implement this interface. The principal implementors are: 67 * 68 * <ul> 69 * <li>{@link NativeATObject}: provides a default implementation for all <i>native</i> data types. 70 * For example, native methods, closures, abstract grammar nodes, booleans, numbers, etc. 71 * are all represented as AmbientTalk objects with 'native' behaviour. 72 * <li>{@link NATCallframe}: overrides most of the default behaviour of {@link NativeATObject} to 73 * implement the behaviour of call frames, also known as <i>activation records</i>. In 74 * AmbientTalk, call frames are the objects that together define the runtime stack. 75 * They are objects with support for fields but without support for actual methods. 76 * <li>{@link NATObject}: extends the behaviour of call frames to include support for 77 * full-fledged, programmer-defined objects with support for methods and delegation. 78 * <li>{@link JavaClass} and {@link JavaObject}: adapt the behaviour of native AmbientTalk 79 * objects to engage in symbiosis with either a Java class or a Java object. 80 * This implementation makes use of the Java Reflection API to regard Java objects 81 * as though it were AmbientTalk objects. 82 * <li>{@link NATMirage} and {@link OBJMirrorRoot}: these two classes work in tandem to 83 * enable reflection on AmbientTalk objects. That is, because of these two classes, an 84 * AmbientTalk programmer can himself invoke the methods provided in this interface. 85 * {@link NATMirage} implements each operation in this interface by forwarding a 86 * downed invocation to a custom so-called <i>mirror</i> object. This mirror object 87 * can delegate to {@link OBJMirrorRoot}, which is a special object that implements 88 * each meta-level operation of this interface as a base-level operation. Hence, in 89 * a sense, {@link OBJMirrorRoot} also 'implements' this interface, but at the 90 * AmbientTalk level, rather than at the Java level. 91 * </ul> 92 * 93 * @author tvcutsem 94 */ 95public interface ATObject extends ATConversions { 96 97 /* ------------------------------ 98 * -- Message Sending Protocol -- 99 * ------------------------------ */ 100 101 /** 102 * This behavioural meta-level operation reifies the act of sending 103 * an asynchronous message. 104 * 105 * When the base-level AmbientTalk code <code>rcv<-m()</code> is 106 * evaluated in the context of an object <tt>o</tt>, an asynchronous message 107 * <code><-m()</code> is first created by the current actor mirror. 108 * Subsequently, this message needs to be sent to the receiver. This 109 * meta-level operation is reified by this method, as if by invoking: 110 * <pre>(reflect: o).send(message)</pre> 111 * The default behaviour is to access the current actor's mirror and to 112 * ask the actor to send the message in this object's stead by invoking 113 * <pre>actor.send(message)</pre> 114 * @param receiver the object designated to receive the asynchronous message 115 * @param message the asynchronous message to be sent by this object 116 * 117 * @return the result of message sending, which will be the value of an 118 * asynchronous message send expression. 119 */ 120 public ATObject meta_send(ATObject receiver, ATAsyncMessage message) throws InterpreterException; 121 122 /** 123 * This behavioural meta-level operation reifies the act of receiving 124 * an asynchronous message. 125 * 126 * When an AmbientTalk object receives a message that was sent to it 127 * asynchronously, the message is delivered to the object's mirror by 128 * means of this meta-level operation. 129 * <p> 130 * The default behaviour of a mirror in response to the reception of a 131 * message <tt>msg</tt> is to invoke: 132 * <pre>msg.process(self)</pre> 133 * In turn, the default message processing behaviour is to invoke 134 * the method corresponding to the message's selector on this object. 135 * Hence, usually a <tt>receive</tt> operation is simply translated into 136 * a <tt>invoke</tt> operation. The reason for having a separate <tt>receive</tt> 137 * operation is that this enables the AmbientTalk meta-level programmer to 138 * distinguish between synchronously and asynchronously received messages. 139 * @param message the message that was asynchronously sent to this object 140 * @return by default, the value of invoking the method corresponding to the message 141 */ 142 public ATObject meta_receive(ATAsyncMessage message) throws InterpreterException; 143 144 /** 145 * This meta-level operation reifies synchronous message sending ("method invocation"). 146 * Hence, the meta-level equivalent 147 * of the base-level code <code>o.m()</code> is: 148 * <pre>(reflect: o).invoke(o,`m,[])</pre>. 149 * 150 * Method invocation comprises selector lookup and the application of the value 151 * bound to the selector. Selector lookup first queries an object's local 152 * fields, then the method dictionary: 153 * <ul> 154 * <li>If the selector ends with <tt>:=</tt> and matches a field, the field 155 * is assigned if a unary argument list is specified (i.e. the field is treated 156 * as a mutator method). 157 * <li>Otherwise, if the selector is bound to a field containing 158 * a closure, that closure is applied to the given arguments. 159 * <li>If the field is not bound to a closure, the field value is returned provided no arguments were 160 * specified (i.e. the field is treated like an accessor method). 161 * <li>If the selector is bound to a method, the method is applied. 162 * <li>If the selector is not found, the search continues in the objects <i>dynamic parent</i>. 163 * </ul> 164 * <p> 165 * Note also that the first argument to <tt>invoke</tt> denotes the 166 * so-called "receiver" of the invocation. It is this object to which 167 * the <tt>self</tt> pseudo-variable should be bound during method execution. 168 * 169 * @see #meta_doesNotUnderstand(ATSymbol) for what happens if the selector 170 * is not found. 171 * 172 * @param receiver the object to which <tt>self</tt> is bound during execution 173 * of the method 174 * @param selector a symbol denoting the name of the method, accessor or mutator to be invoked 175 * @param arguments the table of actual arguments to be passed to the method 176 * @return by default, the object returned from the invoked method 177 */ 178 public ATObject meta_invoke(ATObject receiver, ATSymbol selector, ATTable arguments) throws InterpreterException; 179 180 /** 181 * This meta-level operation reifies "field selection". 182 * In other words, the base-level code 183 * <code>o.m</code> 184 * is interpreted at the meta-level as: 185 * <code>(reflect: o).invokeField(o, `m)</code> 186 * 187 * This meta-level operation is nearly identical to {@link #meta_invoke(ATObject, ATSymbol, ATTable)} with one 188 * important difference. When the selector is bound to a field storing a closure, this meta-level operation 189 * does <b>not</b> auto-apply the closure, but returns the closure instead. 190 * 191 * For all other cases, the following equality holds: 192 * <code>o.m == o.m()</code> 193 * or, at the meta-level: 194 * <code>(reflect: o).invokeField(o, `m) == (reflect: o).invoke(o, `m, [])</code> 195 * 196 * This effectively means that for client objects, it should not matter whether 197 * a property is implemented as a field or as a pair of accessor/mutator methods. 198 * 199 * @param receiver the base-level object from which the 'field' should be selected. 200 * @param selector a symbol denoting the name of the method, accessor or mutator to be invoked 201 * @return the value of a field, or the return value of a nullary method. 202 */ 203 public ATObject meta_invokeField(ATObject receiver, ATSymbol selector) throws InterpreterException; 204 205 /** 206 * This meta-level method is used to determine whether an object has a 207 * field or method corresponding to the given selector, without actually invoking 208 * or selecting any value associated with that selector. 209 * <p> 210 * The lookup process is the same as that for the <tt>invoke</tt> operation (i.e. 211 * not only the object's own fields and methods are searched, but also those of 212 * its dynamic parents). 213 * 214 * @param selector a symbol denoting the name of a field (accessor or mutator) or method 215 * @return a boolean denoting whether the object responds to <tt>o.selector</tt> 216 */ 217 public ATBoolean meta_respondsTo(ATSymbol selector) throws InterpreterException; 218 219 /** 220 * This behavioural meta-level operation reifies a failed dynamic method or field lookup. 221 * 222 * When method invocation or field selection fails to find the selector in 223 * the dynamic parent chain of an object, rather than immediately raising an 224 * {@link XSelectorNotFound} exception, the mirror of the original receiver 225 * of the method invocation or field selection is asked to handle failed lookup. 226 * <p> 227 * The default behaviour of <tt>doesNotUnderstand</tt> is to raise an 228 * {@link XSelectorNotFound} exception. 229 * <p> 230 * This method is very reminiscent of Smalltalk's well-known 231 * <tt>doesNotUnderstand:</tt> and of Ruby's <tt>method_missing</tt> methods. 232 * There are, however, two important differences: 233 * <ul> 234 * <li> <tt>doesNotUnderstand</tt> is a <b>meta</b>-level operation in AmbientTalk. 235 * It is an operation defined on mirrors, not on regular objects. 236 * <li> <tt>doesNotUnderstand</tt> in AmbientTalk relates to <i>attribute 237 * selection</i>, not to <i>method invocation</i>. Hence, this operation is 238 * more general in AmbientTalk than in Smalltalk: it intercepts both failed 239 * method invocations as well as failed field selections. Hence, it can be used 240 * to model "virtual" fields. This shows in the interface: this operation 241 * does not consume the actual arguments of a failed method invocation. Moreover, 242 * a closure should be returned which can subsequently be applied for failed invocations. 243 * Failed selections can simply return this closure without application. Hence, arguments 244 * should be consumed by means of currying, e.g. by making <tt>doesNotUnderstand</tt> 245 * return a block which can then take the arguments table as its sole parameter. 246 * </ul> 247 * 248 * @param selector a symbol denoting the name of a method or field that could not be found 249 * @return by default, this operation does not return a value, but raises an exception instead. 250 * @throws edu.vub.at.exceptions.XSelectorNotFound the default reaction to a failed selection 251 */ 252 public ATClosure meta_doesNotUnderstand(ATSymbol selector) throws InterpreterException; 253 254 /* ----------------------------- 255 * -- Object Passing protocol -- 256 * ----------------------------- */ 257 258 /** 259 * This behavioural meta-level operation reifies object serialization. 260 * 261 * When an AmbientTalk object crosses actor boundaries, e.g. by means of 262 * parameter passing, as a return value or because it was explicitly 263 * exported, this meta-level operation is invoked on the object's mirror. 264 * <p> 265 * This operation allows objects to specify themselves how they should 266 * be parameter-passed during inter-actor communication. The interpreter 267 * will never pass an object to another actor directly, but instead always 268 * parameter-passes the <i>return value</i> of invoing <tt>pass()</tt> on 269 * the object's mirror. 270 * <p> 271 * Mirrors on by-copy objects implement <tt>pass</tt> as follows: 272 * <pre>def pass() { base }</pre> 273 * Mirrors on by-reference objects implement <tt>pass</tt> by returning 274 * a far reference to their base-level object. 275 * 276 * @return the object to be parameter-passed instead of this object. For objects, 277 * the default is a far reference to themselves. For isolates, the default is 278 * to return themselves. 279 */ 280 public ATObject meta_pass() throws InterpreterException; 281 282 /** 283 * This behavioural meta-level operation reifies object deserialization. 284 * 285 * When an AmbientTalk object has just crossed an actor boundary (e.g. 286 * because of inter-actor message sending) this meta-level operation 287 * is invoked on the object's mirror. 288 * <p> 289 * This meta-level operation gives objects a chance to tell the interpreter 290 * which object they actually represent, because the object retained 291 * after parameter passing is the return value of the <tt>resolve</tt> 292 * operation. 293 * <p> 294 * Mirrors on by-copy objects, like isolates, implement <tt>resolve</tt> as follows: 295 * <pre>def resolve() { base }</pre> 296 * In other words, by-copy objects represent themselves. By-reference objects 297 * are paremeter passed as far references. Mirrors on far references implement 298 * <tt>resolve</tt> by trying to resolve the far reference into a local, regular 299 * object reference (which is possible if the object they point to is located 300 * in the actor in which they just arrived). If it is not possible to resolve 301 * a far reference into a local object, the far reference remains a far reference. 302 * <p> 303 * Note that for isolates, this operation also ensures that the isolate's 304 * lexical scope is rebound to the lexical root of the recipient actor. 305 * 306 * @return the object represented by this object 307 * @throws XObjectOffline if a far reference to a local object can no longer be resolved 308 * because the object has been taken offline 309 */ 310 public ATObject meta_resolve() throws InterpreterException; 311 312 /* ------------------------------------------ 313 * -- Slot accessing and mutating protocol -- 314 * ------------------------------------------ */ 315 316 /** 317 * This meta-level operation reifies first-class field or method selection. Hence, the 318 * base-level evaluation of <code>o.&x</code> is interpreted at the meta-level as: 319 * <pre>(reflect: o).select(o, `x)</pre> 320 * 321 * The selector lookup follows the same search rules as those for <tt>invoke</tt>. 322 * That is: first an object's local fields and method dictionary are searched, 323 * and only then the object's <i>dynamic parent</i>. 324 * <p> 325 * The <tt>select</tt> operation can be used to both select fields or methods from 326 * an object. When the selector is bound to a method, the return value of 327 * <tt>select</tt> is a closure that wraps the found method in the object in which 328 * the method was found. This ensures that the method retains its context information, 329 * such as the lexical scope in which it was defined and the value of <tt>self</tt>, which 330 * will be bound to the original receiver, i.e. the first argument of <tt>select</tt>. 331 * <p> 332 * If the selector matches a field, an accessor is returned. If the selector ends with 333 * <tt>:=</tt>, a mutator is returned instead. An accessor is a nullary closure which upon 334 * application yields the field's value. A mutator is a unary closure which upon 335 * application assigns the field to the specified value. 336 * Even for fields already bound to a closure, selecting the field returns an accessor 337 * closure, not the bound closure itself. 338 * 339 * @see #meta_doesNotUnderstand(ATSymbol) for what happens if the selector is not found. 340 * 341 * @param receiver the dynamic receiver of the selection. If the result of the selection is 342 * a method, the closure wrapping the method will bind <tt>self</tt> to this object. 343 * @param selector a symbol denoting the name of the field or method to select. 344 * @return if selector is bound to a field, an accessor or mutator for the field; otherwise if 345 * the selector is bound to a method, a closure wrapping the method. 346 */ 347 public ATClosure meta_select(ATObject receiver, ATSymbol selector) throws InterpreterException; 348 349 /** 350 * This meta-level operation reifies field definition. Hence, the base-level 351 * code <code>def x := v</code> evaluated in a lexical scope <tt>lex</tt> 352 * is interpreted at the meta-level as: 353 * <pre>(reflect: lex).defineField(`x, v)</pre> 354 * 355 * Invoking this meta-level operation on an object's mirror adds a new field 356 * to that object. An object cannot contain two or more fields with the 357 * same name. 358 * 359 * @param name a symbol denoting the name of the new field 360 * @param value the value of the new field 361 * @return nil 362 * @throws edu.vub.at.exceptions.XDuplicateSlot if the object already has a 363 * local field with the given name 364 */ 365 public ATNil meta_defineField(ATSymbol name, ATObject value) throws InterpreterException; 366 367 /* ----------------------------------------- 368 * -- Cloning and instantiation protocol -- 369 * ---------------------------------------- */ 370 371 /** 372 * This meta-level operation reifies the act of cloning the base-level object. 373 * Hence, the code <code>clone: o</code> is interpreted at the meta-level as 374 * <pre>(reflect: o).clone()</pre> 375 * 376 * AmbientTalk's default cloning semantics are based on shallow copying. 377 * A cloned object has copies of the original object's fields, but the values 378 * of the fields are shared between the clones. A clone has the same methods 379 * as the original object. Methods added at a later stage to the original 380 * will not affect the clone's methods and vice versa. This means that each 381 * objects has its own independent fields and methods. 382 * <p> 383 * If the cloned AmbientTalk object contains programmer-defined field objects, 384 * each of these fields is re-instantiated with the clone as a parameter. The 385 * clone is intialized with the re-instantiated fields rather than with the 386 * fields of the original object. This property helps to ensure that each 387 * object has its own independent fields. 388 * <p> 389 * If the object has a <i>shares-a</i> relationship with its parent, the object 390 * and its clone will <b>share</b> the same parent object. Shares-a relationships 391 * are the default in AmbientTalk, and they match with the semantics of 392 * shallow copying: the dynamic parent of an object is a regular field, hence 393 * its contents is shallow-copied. 394 * <p> 395 * If the object has an <i>is-a</i> relationship with its parent object, a 396 * clone of the object will receive a clone of the parent object as its parent. 397 * Hence, is-a relationships "override" the default shallow copying semantics 398 * and recursively clone the parent of an object up to a shares-a relationship. 399 * <p> 400 * If a mirage is cloned, its mirror is automatically re-instantiated with 401 * the new mirage, to ensure that each mirage has its independent mirror. 402 * @return a clone of the mirror's <tt>base</tt> object 403 */ 404 public ATObject meta_clone() throws InterpreterException; 405 406 /** 407 * This meta-level operation reifies instance creation. The default 408 * implementation of an AmbientTalk object's <tt>new</tt> method is: 409 * <pre>def new(@initargs) { (reflect: self).newInstance(initargs) }</pre> 410 * 411 * Creating a new instance of an object is a combination of: 412 * <ul> 413 * <li>creating a clone of the object 414 * <li>initializing the clone by invoking its <tt>init</tt> method 415 * </ul> 416 * 417 * The default implementation is: 418 * <pre>def newInstance(initargs) { 419 * def instance := self.clone(); 420 * instance.init(@initargs); 421 * instance; 422 *} 423 * </pre> 424 * 425 * Instance creation in AmbientTalk is designed to mimick class instantiation 426 * in a class-based language. Instantiating a class <tt>c</tt> requires <i>allocating</i> 427 * a new instance <tt>i</tt> and then invoking the <i>constructor</i> on that 428 * new instance. In AmbientTalk, class allocation is replaced by object 429 * <i>cloning</i>. The benefit is that an instantiated object its variables are 430 * already initialized to useful values, being those of the object from which 431 * it is instantiated. The <tt>init</tt> method plays the role of "constructor" 432 * in AmbientTalk. 433 * 434 * @param initargs a table denoting the actual arguments to be passed to 435 * the <tt>init</tt> method 436 * @return the new instance 437 */ 438 public ATObject meta_newInstance(ATTable initargs) throws InterpreterException; 439 440 /* --------------------------------- 441 * -- Structural Access Protocol -- 442 * --------------------------------- */ 443 444 /** 445 * This structural meta-level operation adds a field object to the receiver mirror's 446 * base object. An object cannot contain two or more fields with the same name. 447 * 448 * Note that the field object passed as an argument serves as a <i>prototype</i> 449 * object: the actual field object added is an <i>instance</i> of the passed field object. 450 * A field object should always have an <tt>init</tt> method that takes as an argument 451 * the new host object to which it is added. This is often useful, as the behaviour 452 * of a field may depend on the object in which it resides. Because <tt>addField</tt> 453 * creates a new instance of the field, this gives the field object a chance to 454 * properly refer to its new host. 455 * <p> 456 * As an example, here is how to add a read-only field <tt>foo</tt> initialized 457 * to <tt>5</tt> to an object <tt>obj</tt>: 458 * <pre>def makeConstantField(nam, val) { 459 * object: { 460 * def new(newHost) { self }; // singleton pattern 461 * def name := nam; 462 * def readField() { val }; 463 * def writeField(newVal) { nil }; 464 * } 465 * }; 466 * (reflect: obj).addField(makeConstantField(`foo, 5)); 467 * </pre> 468 * 469 * @param field the prototype field object whose instance should be added 470 * to the receiver's base object 471 * @return nil 472 * @throws XDuplicateSlot if the base object already has a field with the 473 * same name as the new field 474 */ 475 public ATNil meta_addField(ATField field) throws InterpreterException; 476 477 /** 478 * This structural meta-level operation adds a method to the receiver 479 * mirror's base object. An object cannot contain two or more methods 480 * with the same name. 481 * 482 * @param method a method object to add to the receiver's base object's 483 * method dictionary. 484 * @return nil 485 * @throws XDuplicateSlot if a method with the new method's selector already 486 * exists in the base object. 487 */ 488 public ATNil meta_addMethod(ATMethod method) throws InterpreterException; 489 490 /** 491 * This structural meta-level operation allows the metaprogrammer to reify a 492 * field of the receiver mirror's base object. Hence, unlike <tt>select</tt> 493 * and <tt>lookup</tt>, <tt>grabField</tt> returns a <i>field object</i> rather 494 * than the <i>value</i> bound to the field. For example: one could express 495 * <code>obj.super := val</code> at the meta-level as: 496 * 497 * <pre> 498 * def superField := (reflect: obj).grabField(`super); 499 * superField.writeField(val); 500 * </pre> 501 * 502 * Another important difference between <tt>select</tt>, <tt>lookup</tt> and 503 * <tt>grabField</tt> is that <tt>grabField</tt> only considers the fields 504 * <i>local</i> to the receiver's base object. Fields of lexical or dynamic 505 * parent objects are <i>not</i> considered. 506 * 507 * @param selector a symbol representing the name of the field to select. 508 * @return a mirror on this object's field slot. 509 * @throws XUndefinedSlot if the field cannot be found within the receiver's 510 * base object. 511 */ 512 public ATField meta_grabField(ATSymbol selector) throws InterpreterException; 513 514 /** 515 * This structural meta-level operation allows the metaprogrammer to 516 * reify a method defined on the receiver mirror's base object. Note that, 517 * unlike the <tt>select</tt> or <tt>lookup</tt> operations, <tt>grabMethod</tt> 518 * returns the bare method object, i.e. <i>not</i> a closure wrapping the method. 519 * <p> 520 * Also, unlike <tt>select</tt> and <tt>lookup</tt>, <tt>grabField</tt> only 521 * considers the locally defined methods of an object, methods of lexical or 522 * dynamic parent objects are <i>not</i> considered. 523 * 524 * @param selector a symbol representing the name of the method to grab from 525 * the receiver's base object. 526 * @return the bare method object bound to the given selector. 527 * @throws XSelectorNotFound if the method object cannot be found within the 528 * receiver's base object. 529 */ 530 public ATMethod meta_grabMethod(ATSymbol selector) throws InterpreterException; 531 532 /** 533 * This structural meta-level operation allows access to all of the 534 * fields defined on the receiver mirror's base object. Note that 535 * this method only returns the base object's <i>locally</i> defined 536 * fields. Fields from parent objects are not returned. 537 * 538 * @see ATObject#meta_grabField(ATSymbol) for details about the returned 539 * field objects. 540 * @return a table of field objects (of type {@link ATField}). 541 */ 542 public ATTable meta_listFields() throws InterpreterException; 543 544 /** 545 * This structural meta-level operation allows access to all of the 546 * methods defined on the receiver mirror's base object. Note that 547 * this method only returns the base object's <i>locally</i> defined 548 * methods. Methods from parent objects are not returned. 549 * 550 * @see ATObject#meta_grabMethod(ATSymbol) for details about the returned 551 * method objects. 552 * @return a table of method objects (of type {@link ATMethod}). 553 */ 554 public ATTable meta_listMethods() throws InterpreterException; 555 556 /** 557 * This structural meta-level operation returns whether or not 558 * the receiver mirror's base object is an <i>extension</i> of its 559 * parent object. 560 * <p> 561 * In AmbientTalk, all objects are part of a dynamic parent delegation chain: 562 * each object has a <tt>super</tt> field that denotes the object to which to 563 * delegate messages the object cannot understand itself. There are, however, 564 * two kinds of delegation links: 565 * <ul> 566 * <li><b>IS-A</b> links: this kind of link denotes that the child object is 567 * a true extension of its parent, and cannot meaningfully exist without the 568 * parent's state. When the child is cloned, its parent will be cloned as well. 569 * <li><b>SHARES-A</b> links: this kind of link denotes that the child object 570 * simply delegates to its parent for purposes of sharing or code reuse. The 571 * child can meaningfully exist without the parent's state. When the child is 572 * cloned, the clone will delegate to the same parent. 573 * </ul> 574 * 575 * Examples: 576 * <pre>(reflect: (extend: parent with: code)).isExtensionOfParent() => true 577 *(reflect: (share: parent with: code)).isExtensionOfParent() => false 578 * </pre> 579 * 580 * Note that accessing the dynamic parent itself is not a meta-level operation, 581 * the dynamic parent can simply be accessed from the base level by performing 582 * <code>obj.super</code>. 583 * 584 * @return whether the base object extends its parent object via an 585 * <b>IS-A</b> link or not. 586 */ 587 public ATBoolean meta_isExtensionOfParent() throws InterpreterException; 588 589 /* ------------------------------------------ 590 * -- Abstract Grammar evaluation protocol -- 591 * ------------------------------------------ */ 592 593 /** 594 * This behavioural meta-level operation reifies the evaluation of 595 * abstract grammar objects into values. For objects, this operation 596 * returns the base object itself, signifying that the evaluation 597 * function defined on objects is the identity function. In other words, 598 * objects are <i>self-evaluating</i>. Parse tree objects (first-class 599 * abstract grammar elements), however, have dedicated evaluation 600 * functions. For example, evaluating <code>x</code> is equivalent to 601 * evaluating <code>(reflect: `x).eval(ctx)</code> where <tt>ctx</tt> 602 * is a reification of the current evaluation context. 603 * 604 * @param ctx a context object that stores the current lexical scope and 605 * the current value of <tt>self</tt> 606 * @return the value of the abstract grammar element denoted by this mirror's 607 * base object. 608 * @throws XIllegalUnquote if an unquote abstract grammar element is evaluated. Such 609 * abstract grammar elements should only be encountered in a quoted parse tree. 610 */ 611 public ATObject meta_eval(ATContext ctx) throws InterpreterException; 612 613 /** 614 * This behavioural meta-level operation reifies the quotation of 615 * abstract grammar elements. Regular objects simply return themselves 616 * upon quotation. When an abstract grammar element is quoted, rather 617 * than tree-recursively invoking <tt>eval</tt> on the parse trees, 618 * <tt>quote</tt> is tree-recursively invoked. When encountering 619 * an unquote, <tt>eval</tt> is again invoked on the unquoted subtree, 620 * with the context passed as an argument to <tt>quote</tt>. 621 * 622 * @param ctx a context object passed on to be used in subsequent evaluations. 623 * @throws XIllegalQuote exception whenever an unquote-splice unquotation is discovered 624 * in an Abstract Grammar node where the resulting table cannot be spliced. 625 */ 626 public ATObject meta_quote(ATContext ctx) throws InterpreterException; 627 628 /** 629 * This behavioural meta-level operation reifies the act of printing 630 * the base object in the read-eval-print loop. This operation may be 631 * overridden by mirrors to customise the printed representation of 632 * their base object. 633 * 634 * @return a text value denoting a human-readable representation of the object. 635 */ 636 public NATText meta_print() throws InterpreterException; 637 638 /* ---------------------------------- 639 * -- Object Relational Comparison -- 640 * ---------------------------------- */ 641 642 /** 643 * This meta-level operation determines whether this mirror's base object 644 * is related to the parameter object by a combination of cloning and 645 * extension operators. The default implementation is: 646 * 647 * <pre>def isRelatedTo(object) { 648 * self.isCloneOf(object).or: { (reflect: base.super).isRelatedTo(object) } 649 *}</pre> 650 * 651 * @param object the object to compare this mirror's base object to 652 * @return true if the given object is a clone of the base object or a clone 653 * of the base object's parents. 654 */ 655 public ATBoolean meta_isRelatedTo(ATObject object) throws InterpreterException; 656 657 /** 658 * This meta-level operation determines whether this mirror's base object 659 * is a clone of the parameter object. The <i>is-clone-of</i> relation is transitive, 660 * so if <tt>martin</tt> is a clone of <tt>sally</tt> and <tt>sally</tt> is a clone of 661 * <tt>dolly</tt>, then <tt>martin</tt> is a clone of <tt>dolly</tt> as well. 662 * The relation is reflexive: <tt>dolly</tt> is a clone of itself. 663 * The relation is symmetric: <tt>dolly</tt> is also a clone of <tt>sally</tt>. 664 * 665 * @param other the object to check the is-clone-of relationship with. 666 * @return true if the base object and the parameter object are clones (i.e. one 667 * was created by cloning the other), false otherwise. 668 */ 669 public ATBoolean meta_isCloneOf(ATObject other) throws InterpreterException; 670 671 /* --------------------------------- 672 * -- Type Testing and Querying -- 673 * --------------------------------- */ 674 675 /** 676 * Tests whether the receiver mirror's base object is tagged as a particular type. 677 * 678 * The default implementation first compares the object's local type tags to the given type 679 * by means of the {@link ATTypeTag#base_isSubtypeOf(ATTypeTag)} method. If no local type 680 * is found, the test is applied recursively on this object's dynamic parent. In code: 681 * <pre>def isTaggedAs(type) { 682 * (nil != (self.tagsOf: object).find: { |localType| 683 * localType.isSubtypeOf(type) 684 * }).or: { (reflect: base.super).isTaggedAs(type) } 685 * }; 686 * </pre> 687 * 688 * The primitive method <tt>is: obj taggedAs: type</tt> is defined in terms of this 689 * method: 690 * <pre> 691 * def is: obj taggedAs: type { 692 * (reflect: obj).isTaggedAs(type) 693 *}; 694 * </pre> 695 * 696 * @param type the type tag object to check for 697 * @return true if this mirror's base object or one of its parent objects is tagged 698 * with a subtype of the given type, false otherwise. 699 */ 700 public ATBoolean meta_isTaggedAs(ATTypeTag type) throws InterpreterException; 701 702 /** 703 * Returns all of the local type tags of this object. The primitive method 704 * <tt>tagsOf: obj</tt> is defined in terms of this method: 705 * 706 * <pre> 707 * def tagsOf: obj { 708 * (reflect: obj).typeTags 709 *}; 710 * </pre> 711 * 712 * @return a table of the type tags that were attached directly to this mirror's base 713 * object. The type tags of its parent objects are not returned. 714 */ 715 public ATTable meta_typeTags() throws InterpreterException; 716 717 /* ------------------------------- 718 * - Base Level Object interface - 719 * ------------------------------- */ 720 721 /** 722 * Bound to the dynamic parent of this object. 723 * 724 * The dynamic parent of an object is the object to which failed 725 * selection or invocation requests or type tests are delegated to. 726 * 727 * @return the current dynamic parent of this object. 728 */ 729 public ATObject base_super() throws InterpreterException; 730 731 /** 732 * The identity operator. In AmbientTalk, equality of objects 733 * is by default pointer-equality (i.e. objects are equal only 734 * if they are identical). 735 * 736 * This is a primitive method, present by default in every AmbientTalk 737 * object but redefinable by the programmer. 738 * 739 * @return by default, true if the parameter object and this object are identical, 740 * false otherwise. 741 */ 742 public ATBoolean base__opeql__opeql_(ATObject other) throws InterpreterException; 743 744 /** 745 * The object instantiation method. Note that in class-based OO languages, 746 * this method is usually at the level of the <i>class</i>. In AmbientTalk, 747 * this method is situated at the object-level directly. It can be overridden 748 * to e.g. enforce the singleton pattern or to return instances of other 749 * objects. 750 * 751 * The default implementation of this method is: 752 * <pre>def new(@args) { 753 * (reflect: self).newInstance(@args) 754 *}; 755 * </pre> 756 * 757 * This is a primitive method, present by default in every AmbientTalk 758 * object but redefinable by the programmer. 759 * 760 * @see ATObject#meta_newInstance(ATTable) for a description of object instantiation. 761 * @param initargs the variable argument list to pass to the <tt>init</tt> method. 762 * @return by default, the new instance of this mirror's base object. 763 */ 764 public ATObject base_new(ATObject[] initargs) throws InterpreterException; 765 766 /** 767 * The object initialisation method. In class-based languages, this method 768 * is often called the constructor. AmbientTalk only supports one constructor 769 * per object, but thanks to variable argument lists and optional parameters, 770 * the same flexibility as defining multiple constructors can often be achieved. 771 * Also, by overriding <tt>new</tt>, the developer may invoke additional methods 772 * on newly created objects if this is desirable. 773 * 774 * The default implementation of this method is: 775 * <pre>def init(@args) { 776 * super^init(@args) 777 *}; 778 * </pre> 779 * 780 * This is a primitive method, present by default in every AmbientTalk 781 * object but redefinable by the programmer. 782 * 783 * @see ATObject#meta_newInstance(ATTable) for a description of object initialisation. 784 * @param initargs the arguments to the <tt>init</tt> constructor method. 785 * @return the return value of invoking the <tt>init</tt> method. Note that 786 * this value is <i>discarded</i> when <tt>init</tt> is invoked from the 787 * <tt>newInstance</tt> meta-level operation. 788 */ 789 public ATObject base_init(ATObject[] initargs) throws InterpreterException; 790 791 /* ----------------------------------------- 792 * - Implementation-Level Object interface - 793 * ----------------------------------------- */ 794 795 /** 796 * The <tt>lexicalParent</tt> field of a mirror denotes the lexical parent 797 * pointer of the mirror's base object. The lexical parent is the enclosing 798 * <i>lexical scope</i> in which the object was defined. 799 * 800 * @return the object denoting this mirror's base object's lexically 801 * enclosing scope. 802 */ 803 public ATObject impl_lexicalParent() throws InterpreterException; 804 805 /** 806 * Interprets <code>o.x()</code> or <code>o.m(arg)</code>. 807 * Implements slot access. This method is an implementation-level method (not part of the MOP). 808 * @param receiver the dynamic receiver of the slot invocation. 809 * @param selector a regular symbol denoting the slot accessor. 810 * @param arguments the actual arguments to the slot invocation. 811 * @return the result of applying the accessor. 812 * @throws XArityMismatch if a field accessor is not invoked with exactly zero arguments. 813 */ 814 public ATObject impl_invokeAccessor(ATObject receiver, ATSymbol selector, ATTable arguments) throws InterpreterException; 815 816 /** 817 * Interprets <code>o.x := v</code>. 818 * Implements slot mutation. This method is an implementation-level method (not part of the MOP). 819 * @param receiver the dynamic receiver of the slot invocation. 820 * @param selector an assignment symbol denoting which slot to invoke. 821 * @param arguments the actual arguments to the slot invocation. 822 * @return the result of applying the mutator. 823 * @throws XArityMismatch if a field mutator is not invoked with exactly one argument. 824 */ 825 public ATObject impl_invokeMutator(ATObject receiver, ATAssignmentSymbol selector, ATTable arguments) throws InterpreterException; 826 827 /** 828 * Interprets <code>o.&m</code>. 829 * Implements slot accessor selection. This method is an implementation-level method (not part of the MOP). 830 * @param receiver the dynamic receiver of the slot selection. 831 * @param selector a regular symbol denoting the accessor to select. 832 * @return a closure wrapping the selected method or an accessor for a field. 833 */ 834 public ATClosure impl_selectAccessor(ATObject receiver, ATSymbol selector) throws InterpreterException; 835 836 /** 837 * Interprets <code>o.&m:=</code>. 838 * Implements slot mutator selection. This method is an implementation-level method (not part of the MOP). 839 * @param receiver the dynamic receiver of the slot selection. 840 * @param selector an assignment symbol denoting the mutator to select. 841 * @return a closure representing the mutator of a given slot. 842 */ 843 public ATClosure impl_selectMutator(ATObject receiver, ATAssignmentSymbol selector) throws InterpreterException; 844 845 846 /** 847 * Interprets <code>x := v</code> (equivalent to <code>x:=(v)</code>) or <code>f(v)</code>. 848 * Implements functions calls and lexical access to variables. 849 * This method is an implementation-level method (not part of the MOP). 850 851 * Variable lookup first queries the local fields of this object, then the local 852 * method dictionary. If the selector is not found, the search continues in 853 * this object's <i>lexical parent</i>. Hence, variable lookup follows 854 * <b>lexical scoping rules</b>. 855 * <p> 856 * Similar to the behaviour of <tt>invoke</tt>, if the selector is bound to a 857 * field rather than a method, <tt>call</tt> treats the field as an accessor 858 * or mutator method (depending on the selector). 859 * <p> 860 * Note that, unlike <tt>invoke</tt> and <tt>select</tt>, <tt>call</tt> does 861 * not give rise to the invocation of <tt>doesNotUnderstand</tt> if the selector 862 * was not found. The reason for this is that lexical lookup is a static process 863 * for which it makes less sense to provide dynamic interception facilities. 864 * 865 * @param selector a symbol denoting the name of the field or method to look up lexically. 866 * @param arguments the arguments to the lexically scoped function call. 867 * @return if selector is bound to a field, the value of the field; otherwise if selector 868 * is bound to a method, the return value of the method. 869 * @throws XUndefinedSlot if the selector could not be found in the lexical scope of this object. 870 */ 871 public ATObject impl_call(ATSymbol selector, ATTable arguments) throws InterpreterException; 872 873 /** 874 * Interprets <code>f(v)</code>. 875 * Implements the protocol to access lexical variables and methods. This operation (which is not exposed 876 * as part of the MOP) locates the lexically visible binding with the given selector and will return 877 * the value of the slot. 878 * <p> 879 * When this object has a local slot corresponding to the selector: 880 * <ul> 881 * <li> and the slot contains a method or closure, it will be applied with the given arguments (within a context 882 * where self is bound to this object) 883 * <li> and the slot contains a value and the argumentlist is empty, the value is returned 884 * <li> and the slot contains a value and the argumentlist is not empty, an arity mismatch exception is raised 885 * </ul> 886 * <p> 887 * When no local slot is found, lookup continues along the lexical parent chain. When the lexical chain is 888 * completely traversed, an undefined slot exception is raised. 889 */ 890 public ATObject impl_callAccessor(ATSymbol selector, ATTable arguments) throws InterpreterException; 891 892 /** 893 * Interprets <code>x := v</code> (which is equivalent to <code>x:=(v)</code>. 894 * Implements the protocol to assign lexical variables. This operation (which is not exposed as part of the MOP) 895 * locates slots to assign corresponding to a specific assignment symbol (selector + ":=") and looks for: 896 * <ol> 897 * <li> a mutator method with the specified assignment symbol (i.e. including the ":=") which can then be 898 * invoked with the provided arguments. 899 * <li> a field with a corresponding selector (i.e. without the ":=") which is then treated as if it were 900 * a unary mutator method. 901 * </ol> 902 * 903 * If the slot is a method slot, an {@link XUnassignableField} exception is raised, otherwise the arity of the 904 * arguments is verified (should be precisely 1) and the first argument is used as the new value of the slot. 905 * <p> 906 * When no local slot is found, lookup continues along the lexical parent chain. When the lexical chain is 907 * completely traversed, a selector not found exception is reported. 908 */ 909 public ATObject impl_callMutator(ATAssignmentSymbol selector, ATTable arguments) throws InterpreterException; 910 911 /** 912 * Interprets <code>x</code>. 913 * This method is an implementation-level method (not part of the MOP). 914 * 915 * This method is equivalent to {@link #impl_call(ATSymbol, ATTable)} where 916 * the arguments equal <tt>[]</tt>, except for one case: when the selector 917 * resolves to a field containing a closure, the closure is not auto-applied 918 * with zero arguments, but is instead returned. For all other purposes, 919 * evaluating <tt>m</tt> is equivalent to evaluating <tt>m()</tt> such that 920 * fields and nullary methods can be uniformly accessed. 921 * 922 * @param selector the name of a lexically visible field or method. 923 * @return the value of a field or the return value of an accessor method. 924 */ 925 public ATObject impl_callField(ATSymbol selector) throws InterpreterException; 926 927 /** 928 * Interprets <code>&x</code> or <code>&x:=</code>. 929 * This method is an implementation-level method (not part of the MOP). 930 * 931 * This operation is the lexical counterpart of {@link #meta_select(ATObject, ATSymbol)}. 932 * @param selector the name of a lexically visible field or method. 933 * @return a closure wrapping a method, or an accessor or mutator linked to a lexically visible field. 934 */ 935 public ATClosure impl_lookup(ATSymbol selector) throws InterpreterException; 936 937 /** 938 * Interprets <code>&x</code>. 939 * This method is an implementation-level method (not part of the MOP). 940 * 941 * @param selector the name of a lexically visible field or method. 942 * @return a closure wrapping a method, or an accessor linked to a lexically visible field. 943 */ 944 public ATClosure impl_lookupAccessor(ATSymbol selector) throws InterpreterException; 945 946 /** 947 * Interprets <code>&x:=</code>. 948 * This method is an implementation-level method (not part of the MOP). 949 * 950 * If the selector minus <tt>:=</tt> is bound to a field, the field is assigned 951 * i 952 * @param selector the name of a lexically visible method or of a field (whose name does not have the <tt>:=</tt> prefix). 953 * @return a closure wrapping a method, or a mutator linked to a lexically visible field. 954 */ 955 public ATClosure impl_lookupMutator(ATAssignmentSymbol selector) throws InterpreterException; 956 957 /** 958 * This is a callback method used in AmbientTalk's native equality protocol. 959 * When evaluating <tt>o1 == o2</tt> in AmbientTalk, <tt>o1</tt>'s <tt>==</tt> 960 * method will invoke <tt>o2.identityEquals(o1)</tt>. 961 * 962 * The native implementation can make use of Java's <tt>==</tt> operator where 963 * appropriate. 964 */ 965 public ATBoolean impl_identityEquals(ATObject other) throws InterpreterException; 966 967}