101:, though lexical (static) scoping is far more common. In lexical scoping (or lexical scope; also called static scoping or static scope), if a variable name's scope is a certain block, then its scope is the program text of the block definition: within that block's text, the variable name exists, and is bound to the variable's value, but outside that block's text, the variable name does not exist. By contrast, in dynamic scoping (or dynamic scope), if a variable name's scope is a certain block, then its scope is that block and all functions transitively called by that block (except when overridden again by another declaration); after the block ends, the variable name does not exist. Some languages, like
277:
value to a global (package) variable, which lasts until the end of the enclosing block. However, the variable is visible to any function called from within the block. To create lexically-scoped local variables, use the
69:-derived languages allow any number of nested levels of visibility, with private variables, functions, constants and types hidden within them, either by nested blocks or
109:, allow the programmer to choose static or dynamic scoping when defining or redefining a variable. Examples of languages that use dynamic scoping include
458:(while in perl all scalar values have a $ in front). Note that Ruby only provides built-in support for statically-scoped local variables like Perl's
177:
semantics allow the parameters to act as aliases of the values passed as arguments, allowing the subroutine to modify variables outside its own scope.
450:
as a language was inspired also by Perl, but in this case, the notation was made simpler: a global variable name must be preceded by a $ sign, like
605:
165:
passed to it. In most languages, these local parameters are treated the same as other local variables within the subroutine. In contrast,
571:
265:
is used for local lexically-scoped variables. Since dynamic scoping is less common today, the Perl documentation warns that "
149:
82:
141:
447:
110:
274:
214:
190:
229:
74:
39:
58:
531:
202:
98:
78:
54:
45:
545:
480:
213:
with local scope. In this case, recursive calls to the function also have access to the (single,
133:
217:) variable. In all of the above languages, static variables are declared as such with a special
567:
167:
162:
118:
499:
240:
62:
31:
148:. Hence variables of this scope can be declared, written to, and read, without any risk of
475:
210:
86:
70:
209:) which allows a value to be retained from one call of the function to another – it is a
129:)'s "local" declaration. Most other languages provide lexically scoped local variables.
511:(as of 2009). In particular, see section 6.2.4 “Storage durations of objects”, page 32.
233:
145:
466:. There is at least one library for Ruby that provides dynamically-scoped variables.
599:
157:
198:
173:
122:
144:
calls itself, local variables in each instance of the function are given distinct
27:
Computer programming, a variable only usable in a portion of a program (the scope)
561:
57:
in which it is declared overrides the same variable name in the larger scope. In
106:
520:
232:, because their value remains in memory for the life of the program, but have
137:
114:
50:
17:
454:, while a local variable has simply no $ sign in front of its name, like
257:
supports both dynamic and lexically-scoped local variables. The keyword
61:
with only two levels of visibility, local variables are contrasted with
161:
semantics provide a called subroutine with its own local copy of the
194:
66:
394:
This happens since the global variable $ a is modified to a new
254:
126:
102:
586:
Conrad Irwin. "LSpace: Dynamic scope for Ruby". December 2012
421:
variable would be limited to the static scope of the function
206:
152:
to functions outside of the block in which they are declared.
587:
402:, but the global value is restored upon leaving the scope of
246:, which has several different meanings in various languages.
269:
isn't what most people think of as “local”.". Instead, the
261:
is used to define local dynamically-scoped variables, while
228:
Static locals in global functions have the same lifetime as
431:
Randal L. Schwartz and Tom
Phoenix argue that the operator
81:: variables of local scope are used to avoid issues with
417:
would have printed 1 three times since in that case the
285:
To understand how it works consider the following code:
236:(not global scope), as with automatic local variables.
462:, not dynamically-scoped local variables like Perl's
189:
is available in many mainstream languages (including
426:
422:
403:
399:
560:Randal L. Schwartz and Tom Phoenix (2001-07-01).
546:perldoc.perl.org: perlsub: Private Variables via
532:perldoc.perl.org: perlsub: Temporary Values via
97:Local variables may have a lexical or dynamic
8:
185:A special type of local variable, called a
239:This is distinct from other usages of the
491:
132:In most languages, local variables are
435:should have had a different name like
73:. Local variables are fundamental to
49:. A local variable reference in the
7:
155:Programming languages that employ
25:
140:directly. This means that when a
1:
125:, and the MirBSD Korn shell (
606:Variable (computer science)
566:. O'REILLY. paragraph 4.7.
273:keyword gives a temporary,
622:
588:http://cirw.in/blog/lspace
117:, and the shell languages
65:. On the other hand, many
563:Learning Perl 3rd edition
413:in this case instead of
287:
521:perldoc.perl.org: local
443:Local variables in Ruby
398:(local) meaning inside
250:Local variables in Perl
230:static global variables
181:Static local variables
75:procedural programming
590:Retrieved 2013-10-16.
77:, and more generally
59:programming languages
500:"Current C standard"
215:statically allocated
85:that can occur with
134:automatic variables
79:modular programming
481:Non-local variable
388:this will output:
282:operator instead.
275:dynamically-scoped
142:recursive function
359:"$ a\n"
168:call by reference
16:(Redirected from
613:
591:
584:
578:
577:
557:
551:
549:
543:
537:
535:
529:
523:
518:
512:
510:
506:
504:
496:
465:
461:
457:
453:
438:
434:
428:
425:and not seen by
424:
420:
416:
412:
405:
401:
384:
381:
378:
375:
372:
369:
366:
363:
360:
357:
354:
351:
348:
345:
342:
339:
336:
333:
330:
327:
324:
321:
318:
315:
312:
309:
306:
303:
300:
297:
294:
291:
281:
272:
268:
264:
260:
243:
224:
87:global variables
71:nested functions
63:global variables
32:computer science
21:
621:
620:
616:
615:
614:
612:
611:
610:
596:
595:
594:
585:
581:
574:
559:
558:
554:
547:
544:
540:
533:
530:
526:
519:
515:
508:
502:
498:
497:
493:
489:
476:Global variable
472:
463:
459:
455:
452:$ variable_name
451:
445:
436:
432:
430:
418:
414:
410:
392:
386:
385:
382:
379:
376:
373:
370:
367:
364:
361:
358:
355:
352:
349:
346:
343:
340:
337:
334:
331:
328:
325:
322:
319:
316:
313:
310:
307:
304:
301:
298:
295:
292:
289:
279:
270:
266:
262:
258:
252:
241:
222:
221:keyword (e.g.,
211:static variable
183:
95:
28:
23:
22:
15:
12:
11:
5:
619:
617:
609:
608:
598:
597:
593:
592:
579:
572:
552:
538:
524:
513:
509:(3.61 MB)
490:
488:
485:
484:
483:
478:
471:
468:
444:
441:
390:
288:
251:
248:
234:function scope
182:
179:
136:stored on the
94:
91:
42:that is given
36:local variable
26:
24:
14:
13:
10:
9:
6:
4:
3:
2:
618:
607:
604:
603:
601:
589:
583:
580:
575:
573:0-596-00132-0
569:
565:
564:
556:
553:
550:
542:
539:
536:
528:
525:
522:
517:
514:
501:
495:
492:
486:
482:
479:
477:
474:
473:
469:
467:
456:variable_name
449:
442:
440:
407:
397:
389:
286:
283:
276:
256:
249:
247:
245:
237:
235:
231:
226:
220:
219:storage class
216:
212:
208:
204:
200:
196:
192:
188:
187:static local,
180:
178:
176:
175:
170:
169:
164:
160:
159:
158:call by value
153:
151:
147:
143:
139:
135:
130:
128:
124:
120:
116:
112:
108:
104:
100:
92:
90:
88:
84:
80:
76:
72:
68:
64:
60:
56:
52:
48:
47:
41:
37:
33:
19:
582:
562:
555:
541:
527:
516:
494:
446:
408:
395:
393:
387:
284:
253:
238:
227:
218:
199:Visual Basic
186:
184:
174:call by name
172:
166:
156:
154:
150:side-effects
131:
96:
83:side-effects
43:
35:
29:
107:Common Lisp
18:Local scope
487:References
138:call stack
115:Emacs lisp
396:temporary
163:arguments
146:addresses
600:Category
470:See also
51:function
40:variable
534:local()
244:keyword
570:
507:
409:Using
391:1 2 1
242:static
223:static
203:VB.NET
44:local
503:(PDF)
464:local
433:local
415:local
356:print
314:local
271:local
267:local
259:local
99:scope
93:Scope
67:ALGOL
55:block
46:scope
38:is a
568:ISBN
548:my()
448:Ruby
437:save
255:Perl
205:and
171:and
127:mksh
123:dash
119:bash
111:Logo
105:and
103:Perl
34:, a
427:g()
423:f()
419:$ a
404:f()
400:f()
383:();
377:();
371:();
344:sub
338:();
323:$ a
317:$ a
302:sub
290:$ a
225:).
207:PHP
195:C++
53:or
30:In
602::
460:my
439:.
411:my
406:.
350:()
308:()
280:my
263:my
201:,
197:,
121:,
113:,
89:.
576:.
505:.
429:.
380:g
374:f
368:g
365:}
362:;
353:{
347:g
341:}
335:g
332:;
329:2
326:=
320:;
311:{
305:f
299:;
296:1
293:=
193:/
191:C
20:)
Text is available under the Creative Commons Attribution-ShareAlike License. Additional terms may apply.