-
Notifications
You must be signed in to change notification settings - Fork 17
/
sergeyleschev-design-patterns.html
1497 lines (1303 loc) · 112 KB
/
sergeyleschev-design-patterns.html
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
284
285
286
287
288
289
290
291
292
293
294
295
296
297
298
299
300
301
302
303
304
305
306
307
308
309
310
311
312
313
314
315
316
317
318
319
320
321
322
323
324
325
326
327
328
329
330
331
332
333
334
335
336
337
338
339
340
341
342
343
344
345
346
347
348
349
350
351
352
353
354
355
356
357
358
359
360
361
362
363
364
365
366
367
368
369
370
371
372
373
374
375
376
377
378
379
380
381
382
383
384
385
386
387
388
389
390
391
392
393
394
395
396
397
398
399
400
401
402
403
404
405
406
407
408
409
410
411
412
413
414
415
416
417
418
419
420
421
422
423
424
425
426
427
428
429
430
431
432
433
434
435
436
437
438
439
440
441
442
443
444
445
446
447
448
449
450
451
452
453
454
455
456
457
458
459
460
461
462
463
464
465
466
467
468
469
470
471
472
473
474
475
476
477
478
479
480
481
482
483
484
485
486
487
488
489
490
491
492
493
494
495
496
497
498
499
500
501
502
503
504
505
506
507
508
509
510
511
512
513
514
515
516
517
518
519
520
521
522
523
524
525
526
527
528
529
530
531
532
533
534
535
536
537
538
539
540
541
542
543
544
545
546
547
548
549
550
551
552
553
554
555
556
557
558
559
560
561
562
563
564
565
566
567
568
569
570
571
572
573
574
575
576
577
578
579
580
581
582
583
584
585
586
587
588
589
590
591
592
593
594
595
596
597
598
599
600
601
602
603
604
605
606
607
608
609
610
611
612
613
614
615
616
617
618
619
620
621
622
623
624
625
626
627
628
629
630
631
632
633
634
635
636
637
638
639
640
641
642
643
644
645
646
647
648
649
650
651
652
653
654
655
656
657
658
659
660
661
662
663
664
665
666
667
668
669
670
671
672
673
674
675
676
677
678
679
680
681
682
683
684
685
686
687
688
689
690
691
692
693
694
695
696
697
698
699
700
701
702
703
704
705
706
707
708
709
710
711
712
713
714
715
716
717
718
719
720
721
722
723
724
725
726
727
728
729
730
731
732
733
734
735
736
737
738
739
740
741
742
743
744
745
746
747
748
749
750
751
752
753
754
755
756
757
758
759
760
761
762
763
764
765
766
767
768
769
770
771
772
773
774
775
776
777
778
779
780
781
782
783
784
785
786
787
788
789
790
791
792
793
794
795
796
797
798
799
800
801
802
803
804
805
806
807
808
809
810
811
812
813
814
815
816
817
818
819
820
821
822
823
824
825
826
827
828
829
830
831
832
833
834
835
836
837
838
839
840
841
842
843
844
845
846
847
848
849
850
851
852
853
854
855
856
857
858
859
860
861
862
863
864
865
866
867
868
869
870
871
872
873
874
875
876
877
878
879
880
881
882
883
884
885
886
887
888
889
890
891
892
893
894
895
896
897
898
899
900
901
902
903
904
905
906
907
908
909
910
911
912
913
914
915
916
917
918
919
920
921
922
923
924
925
926
927
928
929
930
931
932
933
934
935
936
937
938
939
940
941
942
943
944
945
946
947
948
949
950
951
952
953
954
955
956
957
958
959
960
961
962
963
964
965
966
967
968
969
970
971
972
973
974
975
976
977
978
979
980
981
982
983
984
985
986
987
988
989
990
991
992
993
994
995
996
997
998
999
1000
<!DOCTYPE html><html>
<head>
<meta charset="utf-8">
<meta name="viewport" content="width=device-width, initial-scale=1, minimal-ui">
<meta name="description" content="Sergey Leschev, Team Lead (Swift, TypeScript, Database). Sergey is a professional who is responsible for the design and construction of websites and apps.">
<meta name="twitter:card" content="summary_large_image">
<meta name="twitter:site" content="@sergeyleschev">
<meta name="twitter:title" content="Sergey Leschev">
<meta name="twitter:description" content="Sergey Leschev, Team Lead (Swift, TypeScript, Database). Sergey is a professional who is responsible for the design and construction of websites and apps.">
<meta name="twitter:image" content="https://pbs.twimg.com/profile_images/1372479346225582088/Qek8o6vC_400x400.jpg">
<meta name="twitter:image:src" content="https://pbs.twimg.com/profile_images/1372479346225582088/Qek8o6vC_400x400.jpg">
<meta name="robots" content="index, archive" />
<meta property="cdc:template_version" content="4.0">
<title>Sergey Leschev - Team Lead</title>
<link rel="icon" type="image/x-icon" href="favicon.ico">
<link rel="shortcut icon" type="image/png" href="favicon-32x32.png"/>
<link rel="manifest" href="site.webmanifest">
<link rel="alternate" href="https://sergeyleschev.github.io" hreflang="en-gb"/>
<link rel="alternate" type="application/rss+xml" title="RSS feed: Sergey Leschev - Team Lead" href="https://sergeyleschev.github.io/rss.xml" />
<link rel="canonical" href="https://sergeyleschev.github.io" />
<!-- <script>
!function(f,b,e,v,n,t,s)
{if(f.fbq)return;n=f.fbq=function(){n.callMethod?
n.callMethod.apply(n,arguments):n.queue.push(arguments)};
if(!f._fbq)f._fbq=n;n.push=n;n.loaded=!0;n.version='2.0';
n.queue=[];t=b.createElement(e);t.async=!0;
t.src=v;s=b.getElementsByTagName(e)[0];
s.parentNode.insertBefore(t,s)}(window, document,'script',
'https://connect.facebook.net/en_US/fbevents.js');
fbq('init', '414247107560114');
fbq('track', 'ViewContent');
</script>
<noscript><img height="1" width="1" style="display:none"
src="https://www.facebook.com/tr?id=414247107560114&ev=ViewContent&noscript=1"
/></noscript> -->
<script type="application/ld+json">
{
"@context": "https://schema.org/",
"@type": "Person",
"name": "Sergey Leschev, Team Lead",
"author": "Sergey Leschev",
"image": "https://avatars.githubusercontent.com/u/23653372?v=4&raw=true",
"description": "Sergey is a professional who is responsible for the design and construction of websites and apps.",
"aggregateRating": {
"@type": "AggregateRating",
"ratingValue": "5.0",
"reviewCount": "1427",
"bestRating": "5",
"worstRating": "3"
}
}
</script>
<meta http-equiv="Content-Security-Policy" content="upgrade-insecure-requests">
<meta name="color-scheme" content="light dark">
<meta name="author" content="Sergey Leschev">
<meta name="keywords" content="sergey leschev, siarhei liashchou, sergeyleschev, senior developer, team lead, cto, swift deverloper, typescript developer, near me job, jobs hiring near me, usaa jobs, jobs, work from home jobs, part time jobs near me, remote jobs, target jobs, hiring jobs, jobs online, jobs part time, google jobs, linked in jobs, linkedin jobs, home depot career, jobs from home, virtual assistant jobs, indeed jobs near me, leader, knowledge, qualifications, education, tips, skills, multitasking, references, success, work, job, tie, challenges, abilities, impress, responsibility, future, weeknesses, benefits, results, team player, strengths, interview, degress, examples, strengths, experienced, problem solver, candidate, agency, objective, initiative, team, dreams, conflict, can-do, training, questions, job, work, career, created, swift, typescript, javascript, sql, nosql, postgresql, oracle, sql server, react, redux, swiftui, objective-c, devops, aws, mongodb, pl/sql, angular, project management, nodejs, nextjs, nestjs, api, agile, amplitude, analytics, appclip, appstore, bash, css, jira, confluence, git, graphql, html, html5, mvp, mvvm, nginx, ssh, prime react, rest, teamcity, typeorm, uikit, uml, viper, widgets, xcode, json, linux, docker, mobx, tvOS, watchOS" />
<link rel="stylesheet" href="github-markdown.css">
<style>
body {
box-sizing: border-box;
min-width: 200px;
max-width: 980px;
margin: 0 auto;
padding: 25px;
}
@media (prefers-color-scheme: dark) {
body {
background-color: #0d1117;
}
}
</style>
<style>
.github-fork-ribbon:before {
background-color: #121612;
}
</style>
</head>
<article id="personal-details" class="markdown-body"><h1> <a href="https://sergeyleschev.github.io"><img itemprop="image" alt="Sergey Leschev" src="apple-touch-icon.png" width=27/></a> Sergey Leschev</h1>
<img itemprop="image" alt="Sergey Leschev" src="https://sergeyleschev.github.io/sergeyleschev.png" width=300/>
<h3>Design Patterns</h3>
<p><a href="https://sergeyleschev.github.io/sergeyleschev-ios-roadmap.html">Swift (L6+)</a> | <a href="https://sergeyleschev.github.io/sergeyleschev-fullstack-roadmap.html">Full Stack (L6+)</a> | <a href="https://sergeyleschev.github.io/sergeyleschev-design-patterns.html">Design Patterns (L6+)</a> | <a href="https://sergeyleschev.github.io/sergeyleschev-system-architect-roadmap.html">System Architect (L7+)</a> | <a href="https://medium.com/@sergeyleschev/lists">Blog</a></p>
<p>Google Engineering Level: L6+</p>
<br>
<h2>🏆 Awards</h2>
<h3>Ranking #Dev: Global TOP 200 (<a href="https://leetcode.com/sergeyleschev/">Certificate</a>)</h3>
<p><a href="https://leetcode.com/sergeyleschev/"><img itemprop="image" alt="Sergey Leschev" src="https://github.com/sergeyleschev/sergeyleschev/blob/main/leetcode-ranking.png?raw=true" width="410"></a></p>
<p><a href="https://leetcode.com/sergeyleschev/"><img itemprop="image" alt="Sergey Leschev" src="https://github.com/sergeyleschev/sergeyleschev/blob/main/leetcode-medals.png?raw=true" width="280"></a></p>
<p><strong>Languages</strong>: Swift, Shell, Database (T-SQL, PL/SQL, MySQL), Concurrency (Python3).</p>
<p><strong>Algorithms</strong>: linked lists, binary search, hash table, queue/stack, dfs/bfs, sort, heap/hash, two pointers, sliding window, tree, greedy problems etc.</p>
<hr>
<div style="page-break-after: always;"></div>
<h3>Golden Award Muad’Dib’s Challenge</h3>
<p><a href="https://app.codility.com/cert/view/cert5YT6JA-Y9ZKFEFXEZWGTR3G/"><img itemprop="image" alt="Sergey Leschev" src="https://github.com/sergeyleschev/sergeyleschev/blob/main/codility-ranking-muaddibs.png?raw=true" width="410"></a></p>
<p><strong>Languages</strong>: Swift.</p>
<p><strong>Algorithmic skills</strong>: Dynamic programming, Greedy algorithms, Binary search, Stack and Queues, Sorting, Time Complexity.</p>
<p><strong>Contest</strong>: Algorithms, Data Structures.</p>
<hr>
<div style="page-break-after: always;"></div>
<h2>Table of Contents</h2>
<table>
<thead>
<tr>
<th><a href="#behavioral">Behavioral</a></th>
<th><a href="#creational">Creational</a></th>
<th><a href="#structural">Structural</a></th>
</tr>
</thead>
<tbody>
<tr>
<td><a href="#-chain-of-responsibility">🐝 Chain Of Responsibility</a></td>
<td><a href="#-abstract-factory">🌰 Abstract Factory</a></td>
<td><a href="#-adapter">🔌 Adapter</a></td>
</tr>
<tr>
<td><a href="#-command">👫 Command</a></td>
<td><a href="#-builder">👷 Builder</a></td>
<td><a href="#-bridge">🌉 Bridge</a></td>
</tr>
<tr>
<td><a href="#-interpreter">🎶 Interpreter</a></td>
<td><a href="#-factory-method">🏭 Factory Method</a></td>
<td><a href="#-composite">🌿 Composite</a></td>
</tr>
<tr>
<td><a href="#-iterator">🍫 Iterator</a></td>
<td><a href="#-monostate">🔂 Monostate</a></td>
<td><a href="#-decorator">🍧 Decorator</a></td>
</tr>
<tr>
<td><a href="#-mediator">💐 Mediator</a></td>
<td><a href="#-prototype">🃏 Prototype</a></td>
<td><a href="#-facade">🎁 Facade</a></td>
</tr>
<tr>
<td><a href="#-memento">💾 Memento</a></td>
<td><a href="#-singleton">💍 Singleton</a></td>
<td><a href="#-flyweight">🍃 Flyweight</a></td>
</tr>
<tr>
<td><a href="#-observer">👓 Observer</a></td>
<td></td>
<td><a href="#-protection-proxy">☔ Protection Proxy</a></td>
</tr>
<tr>
<td><a href="#-state">🐉 State</a></td>
<td></td>
<td><a href="#-virtual-proxy">🍬 Virtual Proxy</a></td>
</tr>
<tr>
<td><a href="#-strategy">💡 Strategy</a></td>
<td></td>
<td></td>
</tr>
<tr>
<td><a href="#-visitor">🏃 Visitor</a></td>
<td></td>
<td></td>
</tr>
<tr>
<td><a href="#-template-method">📝 Template Method</a></td>
<td></td>
<td></td>
</tr>
</tbody>
</table>
<div style="page-break-after: always;"></div>
<h2>Behavioral</h2>
<blockquote>
<p>In software engineering, behavioral design patterns are design patterns that identify common communication patterns between objects and realize these patterns. By doing so, these patterns increase flexibility in carrying out this communication.</p>
<p><strong>Source:</strong> <a href="http://en.wikipedia.org/wiki/Behavioral_pattern">wikipedia.org</a></p>
</blockquote>
<h2>🐝 Chain Of Responsibility</h2>
<p>The chain of responsibility pattern is used to process varied requests, each of which may be dealt with by a different handler.</p>
<h3>Example:</h3>
<pre><code class="language-swift"><span class="hljs-class"><span class="hljs-keyword">protocol</span> <span class="hljs-title">Withdrawing</span> </span>{
<span class="hljs-function"><span class="hljs-keyword">func</span> <span class="hljs-title">withdraw</span><span class="hljs-params">(amount: Int)</span></span> -> <span class="hljs-type">Bool</span>
}
<span class="hljs-keyword">final</span> <span class="hljs-class"><span class="hljs-keyword">class</span> <span class="hljs-title">MoneyPile</span>: <span class="hljs-title">Withdrawing</span> </span>{
<span class="hljs-keyword">let</span> value: <span class="hljs-type">Int</span>
<span class="hljs-keyword">var</span> quantity: <span class="hljs-type">Int</span>
<span class="hljs-keyword">var</span> next: <span class="hljs-type">Withdrawing</span>?
<span class="hljs-keyword">init</span>(value: <span class="hljs-type">Int</span>, quantity: <span class="hljs-type">Int</span>, next: <span class="hljs-type">Withdrawing</span>?) {
<span class="hljs-keyword">self</span>.value = value
<span class="hljs-keyword">self</span>.quantity = quantity
<span class="hljs-keyword">self</span>.next = next
}
<span class="hljs-function"><span class="hljs-keyword">func</span> <span class="hljs-title">withdraw</span><span class="hljs-params">(amount: Int)</span></span> -> <span class="hljs-type">Bool</span> {
<span class="hljs-keyword">var</span> amount = amount
<span class="hljs-function"><span class="hljs-keyword">func</span> <span class="hljs-title">canTakeSomeBill</span><span class="hljs-params">(want: Int)</span></span> -> <span class="hljs-type">Bool</span> {
<span class="hljs-keyword">return</span> (want / <span class="hljs-keyword">self</span>.value) > <span class="hljs-number">0</span>
}
<span class="hljs-keyword">var</span> quantity = <span class="hljs-keyword">self</span>.quantity
<span class="hljs-keyword">while</span> canTakeSomeBill(want: amount) {
<span class="hljs-keyword">if</span> quantity == <span class="hljs-number">0</span> {
<span class="hljs-keyword">break</span>
}
amount -= <span class="hljs-keyword">self</span>.value
quantity -= <span class="hljs-number">1</span>
}
<span class="hljs-keyword">guard</span> amount > <span class="hljs-number">0</span> <span class="hljs-keyword">else</span> {
<span class="hljs-keyword">return</span> <span class="hljs-literal">true</span>
}
<span class="hljs-keyword">if</span> <span class="hljs-keyword">let</span> next = <span class="hljs-keyword">self</span>.next {
<span class="hljs-keyword">return</span> next.withdraw(amount: amount)
}
<span class="hljs-keyword">return</span> <span class="hljs-literal">false</span>
}
}
<span class="hljs-keyword">final</span> <span class="hljs-class"><span class="hljs-keyword">class</span> <span class="hljs-title">ATM</span>: <span class="hljs-title">Withdrawing</span> </span>{
<span class="hljs-keyword">private</span> <span class="hljs-keyword">var</span> hundred: <span class="hljs-type">Withdrawing</span>
<span class="hljs-keyword">private</span> <span class="hljs-keyword">var</span> fifty: <span class="hljs-type">Withdrawing</span>
<span class="hljs-keyword">private</span> <span class="hljs-keyword">var</span> twenty: <span class="hljs-type">Withdrawing</span>
<span class="hljs-keyword">private</span> <span class="hljs-keyword">var</span> ten: <span class="hljs-type">Withdrawing</span>
<span class="hljs-keyword">private</span> <span class="hljs-keyword">var</span> startPile: <span class="hljs-type">Withdrawing</span> {
<span class="hljs-keyword">return</span> <span class="hljs-keyword">self</span>.hundred
}
<span class="hljs-keyword">init</span>(hundred: <span class="hljs-type">Withdrawing</span>,
fifty: <span class="hljs-type">Withdrawing</span>,
twenty: <span class="hljs-type">Withdrawing</span>,
ten: <span class="hljs-type">Withdrawing</span>) {
<span class="hljs-keyword">self</span>.hundred = hundred
<span class="hljs-keyword">self</span>.fifty = fifty
<span class="hljs-keyword">self</span>.twenty = twenty
<span class="hljs-keyword">self</span>.ten = ten
}
<span class="hljs-function"><span class="hljs-keyword">func</span> <span class="hljs-title">withdraw</span><span class="hljs-params">(amount: Int)</span></span> -> <span class="hljs-type">Bool</span> {
<span class="hljs-keyword">return</span> startPile.withdraw(amount: amount)
}
}
</code></pre>
<h3>Usage</h3>
<pre><code class="language-swift"><span class="hljs-comment">// Create piles of money and link them together 10 < 20 < 50 < 100.**</span>
<span class="hljs-keyword">let</span> ten = <span class="hljs-type">MoneyPile</span>(value: <span class="hljs-number">10</span>, quantity: <span class="hljs-number">6</span>, next: <span class="hljs-literal">nil</span>)
<span class="hljs-keyword">let</span> twenty = <span class="hljs-type">MoneyPile</span>(value: <span class="hljs-number">20</span>, quantity: <span class="hljs-number">2</span>, next: ten)
<span class="hljs-keyword">let</span> fifty = <span class="hljs-type">MoneyPile</span>(value: <span class="hljs-number">50</span>, quantity: <span class="hljs-number">2</span>, next: twenty)
<span class="hljs-keyword">let</span> hundred = <span class="hljs-type">MoneyPile</span>(value: <span class="hljs-number">100</span>, quantity: <span class="hljs-number">1</span>, next: fifty)
<span class="hljs-comment">// Build ATM.</span>
<span class="hljs-keyword">var</span> atm = <span class="hljs-type">ATM</span>(hundred: hundred, fifty: fifty, twenty: twenty, ten: ten)
atm.withdraw(amount: <span class="hljs-number">310</span>) <span class="hljs-comment">// Cannot because ATM has only 300</span>
atm.withdraw(amount: <span class="hljs-number">100</span>) <span class="hljs-comment">// Can withdraw - 1x100</span>
</code></pre>
<div style="page-break-after: always;"></div>
<h2>👫 Command</h2>
<p>The command pattern is used to express a request, including the call to be made and all of its required parameters, in a command object. The command may then be executed immediately or held for later use.</p>
<h3>Example:</h3>
<pre><code class="language-swift"><span class="hljs-class"><span class="hljs-keyword">protocol</span> <span class="hljs-title">DoorCommand</span> </span>{
<span class="hljs-function"><span class="hljs-keyword">func</span> <span class="hljs-title">execute</span><span class="hljs-params">()</span></span> -> <span class="hljs-type">String</span>
}
<span class="hljs-keyword">final</span> <span class="hljs-class"><span class="hljs-keyword">class</span> <span class="hljs-title">OpenCommand</span>: <span class="hljs-title">DoorCommand</span> </span>{
<span class="hljs-keyword">let</span> doors:<span class="hljs-type">String</span>
<span class="hljs-keyword">required</span> <span class="hljs-keyword">init</span>(doors: <span class="hljs-type">String</span>) {
<span class="hljs-keyword">self</span>.doors = doors
}
<span class="hljs-function"><span class="hljs-keyword">func</span> <span class="hljs-title">execute</span><span class="hljs-params">()</span></span> -> <span class="hljs-type">String</span> {
<span class="hljs-keyword">return</span> <span class="hljs-string">"Opened \(doors)"</span>
}
}
<span class="hljs-keyword">final</span> <span class="hljs-class"><span class="hljs-keyword">class</span> <span class="hljs-title">CloseCommand</span>: <span class="hljs-title">DoorCommand</span> </span>{
<span class="hljs-keyword">let</span> doors:<span class="hljs-type">String</span>
<span class="hljs-keyword">required</span> <span class="hljs-keyword">init</span>(doors: <span class="hljs-type">String</span>) {
<span class="hljs-keyword">self</span>.doors = doors
}
<span class="hljs-function"><span class="hljs-keyword">func</span> <span class="hljs-title">execute</span><span class="hljs-params">()</span></span> -> <span class="hljs-type">String</span> {
<span class="hljs-keyword">return</span> <span class="hljs-string">"Closed \(doors)"</span>
}
}
<span class="hljs-keyword">final</span> <span class="hljs-class"><span class="hljs-keyword">class</span> <span class="hljs-title">HAL9000DoorsOperations</span> </span>{
<span class="hljs-keyword">let</span> openCommand: <span class="hljs-type">DoorCommand</span>
<span class="hljs-keyword">let</span> closeCommand: <span class="hljs-type">DoorCommand</span>
<span class="hljs-keyword">init</span>(doors: <span class="hljs-type">String</span>) {
<span class="hljs-keyword">self</span>.openCommand = <span class="hljs-type">OpenCommand</span>(doors:doors)
<span class="hljs-keyword">self</span>.closeCommand = <span class="hljs-type">CloseCommand</span>(doors:doors)
}
<span class="hljs-function"><span class="hljs-keyword">func</span> <span class="hljs-title">close</span><span class="hljs-params">()</span></span> -> <span class="hljs-type">String</span> {
<span class="hljs-keyword">return</span> closeCommand.execute()
}
<span class="hljs-function"><span class="hljs-keyword">func</span> <span class="hljs-title">open</span><span class="hljs-params">()</span></span> -> <span class="hljs-type">String</span> {
<span class="hljs-keyword">return</span> openCommand.execute()
}
}
</code></pre>
<h3>Usage:</h3>
<pre><code class="language-swift"><span class="hljs-keyword">let</span> podBayDoors = <span class="hljs-string">"Pod Bay Doors"</span>
<span class="hljs-keyword">let</span> doorModule = <span class="hljs-type">HAL9000DoorsOperations</span>(doors:podBayDoors)
doorModule.<span class="hljs-keyword">open</span>()
doorModule.close()
</code></pre>
<div style="page-break-after: always;"></div>
<h2>🎶 Interpreter</h2>
<p>The interpreter pattern is used to evaluate sentences in a language.</p>
<h3>Example</h3>
<pre><code class="language-swift"><span class="hljs-class"><span class="hljs-keyword">protocol</span> <span class="hljs-title">IntegerExpression</span> </span>{
<span class="hljs-function"><span class="hljs-keyword">func</span> <span class="hljs-title">evaluate</span><span class="hljs-params">(<span class="hljs-number">_</span> context: IntegerContext)</span></span> -> <span class="hljs-type">Int</span>
<span class="hljs-function"><span class="hljs-keyword">func</span> <span class="hljs-title">replace</span><span class="hljs-params">(character: Character, integerExpression: IntegerExpression)</span></span> -> <span class="hljs-type">IntegerExpression</span>
<span class="hljs-function"><span class="hljs-keyword">func</span> <span class="hljs-title">copied</span><span class="hljs-params">()</span></span> -> <span class="hljs-type">IntegerExpression</span>
}
<span class="hljs-keyword">final</span> <span class="hljs-class"><span class="hljs-keyword">class</span> <span class="hljs-title">IntegerContext</span> </span>{
<span class="hljs-keyword">private</span> <span class="hljs-keyword">var</span> data: [<span class="hljs-type">Character</span>:<span class="hljs-type">Int</span>] = [:]
<span class="hljs-function"><span class="hljs-keyword">func</span> <span class="hljs-title">lookup</span><span class="hljs-params">(name: Character)</span></span> -> <span class="hljs-type">Int</span> {
<span class="hljs-keyword">return</span> <span class="hljs-keyword">self</span>.data[name]!
}
<span class="hljs-function"><span class="hljs-keyword">func</span> <span class="hljs-title">assign</span><span class="hljs-params">(expression: IntegerVariableExpression, value: Int)</span></span> {
<span class="hljs-keyword">self</span>.data[expression.name] = value
}
}
<span class="hljs-keyword">final</span> <span class="hljs-class"><span class="hljs-keyword">class</span> <span class="hljs-title">IntegerVariableExpression</span>: <span class="hljs-title">IntegerExpression</span> </span>{
<span class="hljs-keyword">let</span> name: <span class="hljs-type">Character</span>
<span class="hljs-keyword">init</span>(name: <span class="hljs-type">Character</span>) {
<span class="hljs-keyword">self</span>.name = name
}
<span class="hljs-function"><span class="hljs-keyword">func</span> <span class="hljs-title">evaluate</span><span class="hljs-params">(<span class="hljs-number">_</span> context: IntegerContext)</span></span> -> <span class="hljs-type">Int</span> {
<span class="hljs-keyword">return</span> context.lookup(name: <span class="hljs-keyword">self</span>.name)
}
<span class="hljs-function"><span class="hljs-keyword">func</span> <span class="hljs-title">replace</span><span class="hljs-params">(character name: Character, integerExpression: IntegerExpression)</span></span> -> <span class="hljs-type">IntegerExpression</span> {
<span class="hljs-keyword">if</span> name == <span class="hljs-keyword">self</span>.name {
<span class="hljs-keyword">return</span> integerExpression.copied()
} <span class="hljs-keyword">else</span> {
<span class="hljs-keyword">return</span> <span class="hljs-type">IntegerVariableExpression</span>(name: <span class="hljs-keyword">self</span>.name)
}
}
<span class="hljs-function"><span class="hljs-keyword">func</span> <span class="hljs-title">copied</span><span class="hljs-params">()</span></span> -> <span class="hljs-type">IntegerExpression</span> {
<span class="hljs-keyword">return</span> <span class="hljs-type">IntegerVariableExpression</span>(name: <span class="hljs-keyword">self</span>.name)
}
}
<span class="hljs-keyword">final</span> <span class="hljs-class"><span class="hljs-keyword">class</span> <span class="hljs-title">AddExpression</span>: <span class="hljs-title">IntegerExpression</span> </span>{
<span class="hljs-keyword">private</span> <span class="hljs-keyword">var</span> operand1: <span class="hljs-type">IntegerExpression</span>
<span class="hljs-keyword">private</span> <span class="hljs-keyword">var</span> operand2: <span class="hljs-type">IntegerExpression</span>
<span class="hljs-keyword">init</span>(op1: <span class="hljs-type">IntegerExpression</span>, op2: <span class="hljs-type">IntegerExpression</span>) {
<span class="hljs-keyword">self</span>.operand1 = op1
<span class="hljs-keyword">self</span>.operand2 = op2
}
<span class="hljs-function"><span class="hljs-keyword">func</span> <span class="hljs-title">evaluate</span><span class="hljs-params">(<span class="hljs-number">_</span> context: IntegerContext)</span></span> -> <span class="hljs-type">Int</span> {
<span class="hljs-keyword">return</span> <span class="hljs-keyword">self</span>.operand1.evaluate(context) + <span class="hljs-keyword">self</span>.operand2.evaluate(context)
}
<span class="hljs-function"><span class="hljs-keyword">func</span> <span class="hljs-title">replace</span><span class="hljs-params">(character: Character, integerExpression: IntegerExpression)</span></span> -> <span class="hljs-type">IntegerExpression</span> {
<span class="hljs-keyword">return</span> <span class="hljs-type">AddExpression</span>(op1: operand1.replace(character: character, integerExpression: integerExpression),
op2: operand2.replace(character: character, integerExpression: integerExpression))
}
<span class="hljs-function"><span class="hljs-keyword">func</span> <span class="hljs-title">copied</span><span class="hljs-params">()</span></span> -> <span class="hljs-type">IntegerExpression</span> {
<span class="hljs-keyword">return</span> <span class="hljs-type">AddExpression</span>(op1: <span class="hljs-keyword">self</span>.operand1, op2: <span class="hljs-keyword">self</span>.operand2)
}
}
</code></pre>
<h3>Usage</h3>
<pre><code class="language-swift"><span class="hljs-keyword">var</span> context = <span class="hljs-type">IntegerContext</span>()
<span class="hljs-keyword">var</span> a = <span class="hljs-type">IntegerVariableExpression</span>(name: <span class="hljs-string">"A"</span>)
<span class="hljs-keyword">var</span> b = <span class="hljs-type">IntegerVariableExpression</span>(name: <span class="hljs-string">"B"</span>)
<span class="hljs-keyword">var</span> <span class="hljs-built_in">c</span> = <span class="hljs-type">IntegerVariableExpression</span>(name: <span class="hljs-string">"C"</span>)
<span class="hljs-keyword">var</span> expression = <span class="hljs-type">AddExpression</span>(op1: a, op2: <span class="hljs-type">AddExpression</span>(op1: b, op2: <span class="hljs-built_in">c</span>)) <span class="hljs-comment">// a + (b + c)</span>
context.assign(expression: a, value: <span class="hljs-number">2</span>)
context.assign(expression: b, value: <span class="hljs-number">1</span>)
context.assign(expression: <span class="hljs-built_in">c</span>, value: <span class="hljs-number">3</span>)
<span class="hljs-keyword">var</span> result = expression.evaluate(context)
</code></pre>
<h2>🍫 Iterator</h2>
<p>The iterator pattern is used to provide a standard interface for traversing a collection of items in an aggregate object without the need to understand its underlying structure.</p>
<h3>Example:</h3>
<pre><code class="language-swift">
<span class="hljs-class"><span class="hljs-keyword">struct</span> <span class="hljs-title">Novella</span> </span>{
<span class="hljs-keyword">let</span> name: <span class="hljs-type">String</span>
}
<span class="hljs-class"><span class="hljs-keyword">struct</span> <span class="hljs-title">Novellas</span> </span>{
<span class="hljs-keyword">let</span> novellas: [<span class="hljs-type">Novella</span>]
}
<span class="hljs-class"><span class="hljs-keyword">struct</span> <span class="hljs-title">NovellasIterator</span>: <span class="hljs-title">IteratorProtocol</span> </span>{
<span class="hljs-keyword">private</span> <span class="hljs-keyword">var</span> current = <span class="hljs-number">0</span>
<span class="hljs-keyword">private</span> <span class="hljs-keyword">let</span> novellas: [<span class="hljs-type">Novella</span>]
<span class="hljs-keyword">init</span>(novellas: [<span class="hljs-type">Novella</span>]) {
<span class="hljs-keyword">self</span>.novellas = novellas
}
<span class="hljs-keyword">mutating</span> <span class="hljs-function"><span class="hljs-keyword">func</span> <span class="hljs-title">next</span><span class="hljs-params">()</span></span> -> <span class="hljs-type">Novella</span>? {
<span class="hljs-keyword">defer</span> { current += <span class="hljs-number">1</span> }
<span class="hljs-keyword">return</span> novellas.<span class="hljs-built_in">count</span> > current ? novellas[current] : <span class="hljs-literal">nil</span>
}
}
<span class="hljs-class"><span class="hljs-keyword">extension</span> <span class="hljs-title">Novellas</span>: <span class="hljs-title">Sequence</span> </span>{
<span class="hljs-function"><span class="hljs-keyword">func</span> <span class="hljs-title">makeIterator</span><span class="hljs-params">()</span></span> -> <span class="hljs-type">NovellasIterator</span> {
<span class="hljs-keyword">return</span> <span class="hljs-type">NovellasIterator</span>(novellas: novellas)
}
}
</code></pre>
<h3>Usage</h3>
<pre><code class="language-swift"><span class="hljs-keyword">let</span> greatNovellas = <span class="hljs-type">Novellas</span>(novellas: [<span class="hljs-type">Novella</span>(name: <span class="hljs-string">"The Mist"</span>)] )
<span class="hljs-keyword">for</span> novella <span class="hljs-keyword">in</span> greatNovellas {
<span class="hljs-built_in">print</span>(<span class="hljs-string">"I've read: \(novella)"</span>)
}
</code></pre>
<div style="page-break-after: always;"></div>
<h2>💐 Mediator</h2>
<p>The mediator pattern is used to reduce coupling between classes that communicate with each other. Instead of classes communicating directly, and thus requiring knowledge of their implementation, the classes send messages via a mediator object.</p>
<h3>Example</h3>
<pre><code class="language-swift"><span class="hljs-class"><span class="hljs-keyword">protocol</span> <span class="hljs-title">Receiver</span> </span>{
<span class="hljs-keyword">associatedtype</span> <span class="hljs-type">MessageType</span>
<span class="hljs-function"><span class="hljs-keyword">func</span> <span class="hljs-title">receive</span><span class="hljs-params">(message: MessageType)</span></span>
}
<span class="hljs-class"><span class="hljs-keyword">protocol</span> <span class="hljs-title">Sender</span> </span>{
<span class="hljs-keyword">associatedtype</span> <span class="hljs-type">MessageType</span>
<span class="hljs-keyword">associatedtype</span> <span class="hljs-type">ReceiverType</span>: <span class="hljs-type">Receiver</span>
<span class="hljs-keyword">var</span> recipients: [<span class="hljs-type">ReceiverType</span>] { <span class="hljs-keyword">get</span> }
<span class="hljs-function"><span class="hljs-keyword">func</span> <span class="hljs-title">send</span><span class="hljs-params">(message: MessageType)</span></span>
}
<span class="hljs-class"><span class="hljs-keyword">struct</span> <span class="hljs-title">Programmer</span>: <span class="hljs-title">Receiver</span> </span>{
<span class="hljs-keyword">let</span> name: <span class="hljs-type">String</span>
<span class="hljs-keyword">init</span>(name: <span class="hljs-type">String</span>) {
<span class="hljs-keyword">self</span>.name = name
}
<span class="hljs-function"><span class="hljs-keyword">func</span> <span class="hljs-title">receive</span><span class="hljs-params">(message: String)</span></span> {
<span class="hljs-built_in">print</span>(<span class="hljs-string">"\(name) received: \(message)"</span>)
}
}
<span class="hljs-keyword">final</span> <span class="hljs-class"><span class="hljs-keyword">class</span> <span class="hljs-title">MessageMediator</span>: <span class="hljs-title">Sender</span> </span>{
<span class="hljs-keyword">internal</span> <span class="hljs-keyword">var</span> recipients: [<span class="hljs-type">Programmer</span>] = []
<span class="hljs-function"><span class="hljs-keyword">func</span> <span class="hljs-title">add</span><span class="hljs-params">(recipient: Programmer)</span></span> {
recipients.append(recipient)
}
<span class="hljs-function"><span class="hljs-keyword">func</span> <span class="hljs-title">send</span><span class="hljs-params">(message: String)</span></span> {
<span class="hljs-keyword">for</span> recipient <span class="hljs-keyword">in</span> recipients {
recipient.receive(message: message)
}
}
}
</code></pre>
<h3>Usage</h3>
<pre><code class="language-swift"><span class="hljs-function"><span class="hljs-keyword">func</span> <span class="hljs-title">spamMonster</span><span class="hljs-params">(message: String, worker: MessageMediator)</span></span> {
worker.send(message: message)
}
<span class="hljs-keyword">let</span> messagesMediator = <span class="hljs-type">MessageMediator</span>()
<span class="hljs-keyword">let</span> user0 = <span class="hljs-type">Programmer</span>(name: <span class="hljs-string">"Linus Torvalds"</span>)
<span class="hljs-keyword">let</span> user1 = <span class="hljs-type">Programmer</span>(name: <span class="hljs-string">"Avadis 'Avie' Tevanian"</span>)
messagesMediator.add(recipient: user0)
messagesMediator.add(recipient: user1)
spamMonster(message: <span class="hljs-string">"I'd Like to Add you to My Professional Network"</span>, worker: messagesMediator)
</code></pre>
<div style="page-break-after: always;"></div>
<h2>💾 Memento</h2>
<p>The memento pattern is used to capture the current state of an object and store it in such a manner that it can be restored at a later time without breaking the rules of encapsulation.</p>
<h3>Example</h3>
<pre><code class="language-swift"><span class="hljs-keyword">typealias</span> <span class="hljs-type">Memento</span> = [<span class="hljs-type">String</span>: <span class="hljs-type">String</span>]
</code></pre>
<p>Originator</p>
<pre><code class="language-swift"><span class="hljs-class"><span class="hljs-keyword">protocol</span> <span class="hljs-title">MementoConvertible</span> </span>{
<span class="hljs-keyword">var</span> memento: <span class="hljs-type">Memento</span> { <span class="hljs-keyword">get</span> }
<span class="hljs-keyword">init</span>?(memento: <span class="hljs-type">Memento</span>)
}
<span class="hljs-class"><span class="hljs-keyword">struct</span> <span class="hljs-title">GameState</span>: <span class="hljs-title">MementoConvertible</span> </span>{
<span class="hljs-keyword">private</span> <span class="hljs-class"><span class="hljs-keyword">enum</span> <span class="hljs-title">Keys</span> </span>{
<span class="hljs-keyword">static</span> <span class="hljs-keyword">let</span> chapter = <span class="hljs-string">"com.valve.halflife.chapter"</span>
<span class="hljs-keyword">static</span> <span class="hljs-keyword">let</span> weapon = <span class="hljs-string">"com.valve.halflife.weapon"</span>
}
<span class="hljs-keyword">var</span> chapter: <span class="hljs-type">String</span>
<span class="hljs-keyword">var</span> weapon: <span class="hljs-type">String</span>
<span class="hljs-keyword">init</span>(chapter: <span class="hljs-type">String</span>, weapon: <span class="hljs-type">String</span>) {
<span class="hljs-keyword">self</span>.chapter = chapter
<span class="hljs-keyword">self</span>.weapon = weapon
}
<span class="hljs-keyword">init</span>?(memento: <span class="hljs-type">Memento</span>) {
<span class="hljs-keyword">guard</span> <span class="hljs-keyword">let</span> mementoChapter = memento[<span class="hljs-type">Keys</span>.chapter],
<span class="hljs-keyword">let</span> mementoWeapon = memento[<span class="hljs-type">Keys</span>.weapon] <span class="hljs-keyword">else</span> {
<span class="hljs-keyword">return</span> <span class="hljs-literal">nil</span>
}
chapter = mementoChapter
weapon = mementoWeapon
}
<span class="hljs-keyword">var</span> memento: <span class="hljs-type">Memento</span> {
<span class="hljs-keyword">return</span> [ <span class="hljs-type">Keys</span>.chapter: chapter, <span class="hljs-type">Keys</span>.weapon: weapon ]
}
}
</code></pre>
<p>Caretaker</p>
<pre><code class="language-swift"><span class="hljs-class"><span class="hljs-keyword">enum</span> <span class="hljs-title">CheckPoint</span> </span>{
<span class="hljs-keyword">private</span> <span class="hljs-keyword">static</span> <span class="hljs-keyword">let</span> defaults = <span class="hljs-type">UserDefaults</span>.standard
<span class="hljs-keyword">static</span> <span class="hljs-function"><span class="hljs-keyword">func</span> <span class="hljs-title">save</span><span class="hljs-params">(<span class="hljs-number">_</span> state: MementoConvertible, saveName: String)</span></span> {
defaults.<span class="hljs-keyword">set</span>(state.memento, forKey: saveName)
defaults.synchronize()
}
<span class="hljs-keyword">static</span> <span class="hljs-function"><span class="hljs-keyword">func</span> <span class="hljs-title">restore</span><span class="hljs-params">(saveName: String)</span></span> -> <span class="hljs-type">Any</span>? {
<span class="hljs-keyword">return</span> defaults.object(forKey: saveName)
}
}
</code></pre>
<div style="page-break-after: always;"></div>
<h3>Usage</h3>
<pre><code class="language-swift"><span class="hljs-keyword">var</span> gameState = <span class="hljs-type">GameState</span>(chapter: <span class="hljs-string">"Black Mesa Inbound"</span>, weapon: <span class="hljs-string">"Crowbar"</span>)
gameState.chapter = <span class="hljs-string">"Anomalous Materials"</span>
gameState.weapon = <span class="hljs-string">"Glock 17"</span>
<span class="hljs-type">CheckPoint</span>.save(gameState, saveName: <span class="hljs-string">"gameState1"</span>)
gameState.chapter = <span class="hljs-string">"Unforeseen Consequences"</span>
gameState.weapon = <span class="hljs-string">"MP5"</span>
<span class="hljs-type">CheckPoint</span>.save(gameState, saveName: <span class="hljs-string">"gameState2"</span>)
gameState.chapter = <span class="hljs-string">"Office Complex"</span>
gameState.weapon = <span class="hljs-string">"Crossbow"</span>
<span class="hljs-type">CheckPoint</span>.save(gameState, saveName: <span class="hljs-string">"gameState3"</span>)
<span class="hljs-keyword">if</span> <span class="hljs-keyword">let</span> memento = <span class="hljs-type">CheckPoint</span>.restore(saveName: <span class="hljs-string">"gameState1"</span>) <span class="hljs-keyword">as</span>? <span class="hljs-type">Memento</span> {
<span class="hljs-keyword">let</span> finalState = <span class="hljs-type">GameState</span>(memento: memento)
<span class="hljs-built_in">dump</span>(finalState)
}
</code></pre>
<div style="page-break-after: always;"></div>
<h2>👓 Observer</h2>
<p>The observer pattern is used to allow an object to publish changes to its state.
Other objects subscribe to be immediately notified of any changes.</p>
<h3>Example</h3>
<pre><code class="language-swift"><span class="hljs-class"><span class="hljs-keyword">protocol</span> <span class="hljs-title">PropertyObserver</span> : <span class="hljs-title">class</span> </span>{
<span class="hljs-function"><span class="hljs-keyword">func</span> <span class="hljs-title">willChange</span><span class="hljs-params">(propertyName: String, newPropertyValue: <span class="hljs-keyword">Any</span>?)</span></span>
<span class="hljs-function"><span class="hljs-keyword">func</span> <span class="hljs-title">didChange</span><span class="hljs-params">(propertyName: String, oldPropertyValue: <span class="hljs-keyword">Any</span>?)</span></span>
}
<span class="hljs-keyword">final</span> <span class="hljs-class"><span class="hljs-keyword">class</span> <span class="hljs-title">TestChambers</span> </span>{
<span class="hljs-keyword">weak</span> <span class="hljs-keyword">var</span> observer:<span class="hljs-type">PropertyObserver</span>?
<span class="hljs-keyword">private</span> <span class="hljs-keyword">let</span> testChamberNumberName = <span class="hljs-string">"testChamberNumber"</span>
<span class="hljs-keyword">var</span> testChamberNumber: <span class="hljs-type">Int</span> = <span class="hljs-number">0</span> {
<span class="hljs-keyword">willSet</span>(newValue) {
observer?.willChange(propertyName: testChamberNumberName, newPropertyValue: newValue)
}
<span class="hljs-keyword">didSet</span> {
observer?.didChange(propertyName: testChamberNumberName, oldPropertyValue: oldValue)
}
}
}
<span class="hljs-keyword">final</span> <span class="hljs-class"><span class="hljs-keyword">class</span> <span class="hljs-title">Observer</span> : <span class="hljs-title">PropertyObserver</span> </span>{
<span class="hljs-function"><span class="hljs-keyword">func</span> <span class="hljs-title">willChange</span><span class="hljs-params">(propertyName: String, newPropertyValue: <span class="hljs-keyword">Any</span>?)</span></span> {
<span class="hljs-keyword">if</span> newPropertyValue <span class="hljs-keyword">as</span>? <span class="hljs-type">Int</span> == <span class="hljs-number">1</span> {
<span class="hljs-built_in">print</span>(<span class="hljs-string">"Okay. Look."</span>)
}
}
<span class="hljs-function"><span class="hljs-keyword">func</span> <span class="hljs-title">didChange</span><span class="hljs-params">(propertyName: String, oldPropertyValue: <span class="hljs-keyword">Any</span>?)</span></span> {
<span class="hljs-keyword">if</span> oldPropertyValue <span class="hljs-keyword">as</span>? <span class="hljs-type">Int</span> == <span class="hljs-number">0</span> {
<span class="hljs-built_in">print</span>(<span class="hljs-string">"Sorry about the mess."</span>)
}
}
}
</code></pre>
<h3>Usage</h3>
<pre><code class="language-swift"><span class="hljs-keyword">var</span> observerInstance = <span class="hljs-type">Observer</span>()
<span class="hljs-keyword">var</span> testChambers = <span class="hljs-type">TestChambers</span>()
testChambers.observer = observerInstance
testChambers.testChamberNumber += <span class="hljs-number">1</span>
</code></pre>
<h2>🐉 State</h2>
<p>The state pattern is used to alter the behaviour of an object as its internal state changes.
The pattern allows the class for an object to apparently change at run-time.</p>
<h3>Example</h3>
<pre><code class="language-swift"><span class="hljs-keyword">final</span> <span class="hljs-class"><span class="hljs-keyword">class</span> <span class="hljs-title">Context</span> </span>{
<span class="hljs-keyword">private</span> <span class="hljs-keyword">var</span> state: <span class="hljs-type">State</span> = <span class="hljs-type">UnauthorizedState</span>()
<span class="hljs-keyword">var</span> isAuthorized: <span class="hljs-type">Bool</span> {
<span class="hljs-keyword">get</span> { <span class="hljs-keyword">return</span> state.isAuthorized(context: <span class="hljs-keyword">self</span>) }
}
<span class="hljs-keyword">var</span> userId: <span class="hljs-type">String</span>? {
<span class="hljs-keyword">get</span> { <span class="hljs-keyword">return</span> state.userId(context: <span class="hljs-keyword">self</span>) }
}
<span class="hljs-function"><span class="hljs-keyword">func</span> <span class="hljs-title">changeStateToAuthorized</span><span class="hljs-params">(userId: String)</span></span> {
state = <span class="hljs-type">AuthorizedState</span>(userId: userId)
}
<span class="hljs-function"><span class="hljs-keyword">func</span> <span class="hljs-title">changeStateToUnauthorized</span><span class="hljs-params">()</span></span> {
state = <span class="hljs-type">UnauthorizedState</span>()
}
}
<span class="hljs-class"><span class="hljs-keyword">protocol</span> <span class="hljs-title">State</span> </span>{
<span class="hljs-function"><span class="hljs-keyword">func</span> <span class="hljs-title">isAuthorized</span><span class="hljs-params">(context: Context)</span></span> -> <span class="hljs-type">Bool</span>
<span class="hljs-function"><span class="hljs-keyword">func</span> <span class="hljs-title">userId</span><span class="hljs-params">(context: Context)</span></span> -> <span class="hljs-type">String</span>?
}
<span class="hljs-class"><span class="hljs-keyword">class</span> <span class="hljs-title">UnauthorizedState</span>: <span class="hljs-title">State</span> </span>{
<span class="hljs-function"><span class="hljs-keyword">func</span> <span class="hljs-title">isAuthorized</span><span class="hljs-params">(context: Context)</span></span> -> <span class="hljs-type">Bool</span> { <span class="hljs-keyword">return</span> <span class="hljs-literal">false</span> }
<span class="hljs-function"><span class="hljs-keyword">func</span> <span class="hljs-title">userId</span><span class="hljs-params">(context: Context)</span></span> -> <span class="hljs-type">String</span>? { <span class="hljs-keyword">return</span> <span class="hljs-literal">nil</span> }
}
<span class="hljs-class"><span class="hljs-keyword">class</span> <span class="hljs-title">AuthorizedState</span>: <span class="hljs-title">State</span> </span>{
<span class="hljs-keyword">let</span> userId: <span class="hljs-type">String</span>
<span class="hljs-keyword">init</span>(userId: <span class="hljs-type">String</span>) { <span class="hljs-keyword">self</span>.userId = userId }
<span class="hljs-function"><span class="hljs-keyword">func</span> <span class="hljs-title">isAuthorized</span><span class="hljs-params">(context: Context)</span></span> -> <span class="hljs-type">Bool</span> { <span class="hljs-keyword">return</span> <span class="hljs-literal">true</span> }
<span class="hljs-function"><span class="hljs-keyword">func</span> <span class="hljs-title">userId</span><span class="hljs-params">(context: Context)</span></span> -> <span class="hljs-type">String</span>? { <span class="hljs-keyword">return</span> userId }
}
</code></pre>
<h3>Usage</h3>
<pre><code class="language-swift"><span class="hljs-keyword">let</span> userContext = <span class="hljs-type">Context</span>()
(userContext.isAuthorized, userContext.userId)
userContext.changeStateToAuthorized(userId: <span class="hljs-string">"admin"</span>)
(userContext.isAuthorized, userContext.userId) <span class="hljs-comment">// now logged in as "admin"</span>
userContext.changeStateToUnauthorized()
(userContext.isAuthorized, userContext.userId)
</code></pre>
<h2>💡 Strategy</h2>
<p>The strategy pattern is used to create an interchangeable family of algorithms from which the required process is chosen at run-time.</p>
<h3>Example</h3>
<pre><code class="language-swift"><span class="hljs-class"><span class="hljs-keyword">struct</span> <span class="hljs-title">TestSubject</span> </span>{
<span class="hljs-keyword">let</span> pupilDiameter: <span class="hljs-type">Double</span>
<span class="hljs-keyword">let</span> blushResponse: <span class="hljs-type">Double</span>
<span class="hljs-keyword">let</span> isOrganic: <span class="hljs-type">Bool</span>
}
<span class="hljs-class"><span class="hljs-keyword">protocol</span> <span class="hljs-title">RealnessTesting</span>: <span class="hljs-title">AnyObject</span> </span>{
<span class="hljs-function"><span class="hljs-keyword">func</span> <span class="hljs-title">testRealness</span><span class="hljs-params">(<span class="hljs-number">_</span> testSubject: TestSubject)</span></span> -> <span class="hljs-type">Bool</span>
}
<span class="hljs-keyword">final</span> <span class="hljs-class"><span class="hljs-keyword">class</span> <span class="hljs-title">VoightKampffTest</span>: <span class="hljs-title">RealnessTesting</span> </span>{
<span class="hljs-function"><span class="hljs-keyword">func</span> <span class="hljs-title">testRealness</span><span class="hljs-params">(<span class="hljs-number">_</span> testSubject: TestSubject)</span></span> -> <span class="hljs-type">Bool</span> {
<span class="hljs-keyword">return</span> testSubject.pupilDiameter < <span class="hljs-number">30.0</span> || testSubject.blushResponse == <span class="hljs-number">0.0</span>
}
}
<span class="hljs-keyword">final</span> <span class="hljs-class"><span class="hljs-keyword">class</span> <span class="hljs-title">GeneticTest</span>: <span class="hljs-title">RealnessTesting</span> </span>{
<span class="hljs-function"><span class="hljs-keyword">func</span> <span class="hljs-title">testRealness</span><span class="hljs-params">(<span class="hljs-number">_</span> testSubject: TestSubject)</span></span> -> <span class="hljs-type">Bool</span> {
<span class="hljs-keyword">return</span> testSubject.isOrganic
}
}
<span class="hljs-keyword">final</span> <span class="hljs-class"><span class="hljs-keyword">class</span> <span class="hljs-title">BladeRunner</span> </span>{
<span class="hljs-keyword">private</span> <span class="hljs-keyword">let</span> strategy: <span class="hljs-type">RealnessTesting</span>
<span class="hljs-keyword">init</span>(test: <span class="hljs-type">RealnessTesting</span>) { <span class="hljs-keyword">self</span>.strategy = test }
<span class="hljs-function"><span class="hljs-keyword">func</span> <span class="hljs-title">testIfAndroid</span><span class="hljs-params">(<span class="hljs-number">_</span> testSubject: TestSubject)</span></span> -> <span class="hljs-type">Bool</span> {
<span class="hljs-keyword">return</span> !strategy.testRealness(testSubject)
}
}
</code></pre>
<h3>Usage</h3>
<pre><code class="language-swift"><span class="hljs-keyword">let</span> rachel = <span class="hljs-type">TestSubject</span>(pupilDiameter: <span class="hljs-number">30.2</span>,
blushResponse: <span class="hljs-number">0.3</span>,
isOrganic: <span class="hljs-literal">false</span>)
<span class="hljs-comment">// Deckard is using a traditional test</span>
<span class="hljs-keyword">let</span> deckard = <span class="hljs-type">BladeRunner</span>(test: <span class="hljs-type">VoightKampffTest</span>())
<span class="hljs-keyword">let</span> isRachelAndroid = deckard.testIfAndroid(rachel)
<span class="hljs-comment">// Gaff is using a very precise method</span>
<span class="hljs-keyword">let</span> gaff = <span class="hljs-type">BladeRunner</span>(test: <span class="hljs-type">GeneticTest</span>())
<span class="hljs-keyword">let</span> isDeckardAndroid = gaff.testIfAndroid(rachel)
</code></pre>
<h2>📝 Template Method</h2>
<p>The template method pattern defines the steps of an algorithm and allows the redefinition of one or more of these steps. In this way, the template method protects the algorithm, the order of execution and provides abstract methods that can be implemented by concrete types.</p>
<h3>Example</h3>
<pre><code class="language-swift">
<span class="hljs-class"><span class="hljs-keyword">protocol</span> <span class="hljs-title">Garden</span> </span>{
<span class="hljs-function"><span class="hljs-keyword">func</span> <span class="hljs-title">prepareSoil</span><span class="hljs-params">()</span></span>
<span class="hljs-function"><span class="hljs-keyword">func</span> <span class="hljs-title">plantSeeds</span><span class="hljs-params">()</span></span>
<span class="hljs-function"><span class="hljs-keyword">func</span> <span class="hljs-title">waterPlants</span><span class="hljs-params">()</span></span>
<span class="hljs-function"><span class="hljs-keyword">func</span> <span class="hljs-title">prepareGarden</span><span class="hljs-params">()</span></span>
}
<span class="hljs-class"><span class="hljs-keyword">extension</span> <span class="hljs-title">Garden</span> </span>{
<span class="hljs-function"><span class="hljs-keyword">func</span> <span class="hljs-title">prepareGarden</span><span class="hljs-params">()</span></span> {
prepareSoil()
plantSeeds()
waterPlants()
}
}
<span class="hljs-keyword">final</span> <span class="hljs-class"><span class="hljs-keyword">class</span> <span class="hljs-title">RoseGarden</span>: <span class="hljs-title">Garden</span> </span>{
<span class="hljs-function"><span class="hljs-keyword">func</span> <span class="hljs-title">prepare</span><span class="hljs-params">()</span></span> {
prepareGarden()
}
<span class="hljs-function"><span class="hljs-keyword">func</span> <span class="hljs-title">prepareSoil</span><span class="hljs-params">()</span></span> {
<span class="hljs-built_in">print</span> (<span class="hljs-string">"prepare soil for rose garden"</span>)
}
<span class="hljs-function"><span class="hljs-keyword">func</span> <span class="hljs-title">plantSeeds</span><span class="hljs-params">()</span></span> {
<span class="hljs-built_in">print</span> (<span class="hljs-string">"plant seeds for rose garden"</span>)
}
<span class="hljs-function"><span class="hljs-keyword">func</span> <span class="hljs-title">waterPlants</span><span class="hljs-params">()</span></span> {
<span class="hljs-built_in">print</span> (<span class="hljs-string">"water the rose garden"</span>)
}
}
</code></pre>
<h3>Usage</h3>
<pre><code class="language-swift"><span class="hljs-keyword">let</span> roseGarden = <span class="hljs-type">RoseGarden</span>()
roseGarden.prepare()
</code></pre>
<div style="page-break-after: always;"></div>
<h2>🏃 Visitor</h2>
<p>The visitor pattern is used to separate a relatively complex set of structured data classes from the functionality that may be performed upon the data that they hold.</p>
<h3>Example</h3>
<pre><code class="language-swift"><span class="hljs-class"><span class="hljs-keyword">protocol</span> <span class="hljs-title">PlanetVisitor</span> </span>{
<span class="hljs-function"><span class="hljs-keyword">func</span> <span class="hljs-title">visit</span><span class="hljs-params">(planet: PlanetAlderaan)</span></span>
<span class="hljs-function"><span class="hljs-keyword">func</span> <span class="hljs-title">visit</span><span class="hljs-params">(planet: PlanetCoruscant)</span></span>
<span class="hljs-function"><span class="hljs-keyword">func</span> <span class="hljs-title">visit</span><span class="hljs-params">(planet: PlanetTatooine)</span></span>
<span class="hljs-function"><span class="hljs-keyword">func</span> <span class="hljs-title">visit</span><span class="hljs-params">(planet: MoonJedha)</span></span>
}
<span class="hljs-class"><span class="hljs-keyword">protocol</span> <span class="hljs-title">Planet</span> </span>{
<span class="hljs-function"><span class="hljs-keyword">func</span> <span class="hljs-title">accept</span><span class="hljs-params">(visitor: PlanetVisitor)</span></span>
}
<span class="hljs-keyword">final</span> <span class="hljs-class"><span class="hljs-keyword">class</span> <span class="hljs-title">MoonJedha</span>: <span class="hljs-title">Planet</span> </span>{
<span class="hljs-function"><span class="hljs-keyword">func</span> <span class="hljs-title">accept</span><span class="hljs-params">(visitor: PlanetVisitor)</span></span> { visitor.visit(planet: <span class="hljs-keyword">self</span>) }
}
<span class="hljs-keyword">final</span> <span class="hljs-class"><span class="hljs-keyword">class</span> <span class="hljs-title">PlanetAlderaan</span>: <span class="hljs-title">Planet</span> </span>{
<span class="hljs-function"><span class="hljs-keyword">func</span> <span class="hljs-title">accept</span><span class="hljs-params">(visitor: PlanetVisitor)</span></span> { visitor.visit(planet: <span class="hljs-keyword">self</span>) }
}
<span class="hljs-keyword">final</span> <span class="hljs-class"><span class="hljs-keyword">class</span> <span class="hljs-title">PlanetCoruscant</span>: <span class="hljs-title">Planet</span> </span>{
<span class="hljs-function"><span class="hljs-keyword">func</span> <span class="hljs-title">accept</span><span class="hljs-params">(visitor: PlanetVisitor)</span></span> { visitor.visit(planet: <span class="hljs-keyword">self</span>) }
}
<span class="hljs-keyword">final</span> <span class="hljs-class"><span class="hljs-keyword">class</span> <span class="hljs-title">PlanetTatooine</span>: <span class="hljs-title">Planet</span> </span>{
<span class="hljs-function"><span class="hljs-keyword">func</span> <span class="hljs-title">accept</span><span class="hljs-params">(visitor: PlanetVisitor)</span></span> { visitor.visit(planet: <span class="hljs-keyword">self</span>) }
}
<span class="hljs-keyword">final</span> <span class="hljs-class"><span class="hljs-keyword">class</span> <span class="hljs-title">NameVisitor</span>: <span class="hljs-title">PlanetVisitor</span> </span>{
<span class="hljs-keyword">var</span> name = <span class="hljs-string">""</span>
<span class="hljs-function"><span class="hljs-keyword">func</span> <span class="hljs-title">visit</span><span class="hljs-params">(planet: PlanetAlderaan)</span></span> { name = <span class="hljs-string">"Alderaan"</span> }
<span class="hljs-function"><span class="hljs-keyword">func</span> <span class="hljs-title">visit</span><span class="hljs-params">(planet: PlanetCoruscant)</span></span> { name = <span class="hljs-string">"Coruscant"</span> }
<span class="hljs-function"><span class="hljs-keyword">func</span> <span class="hljs-title">visit</span><span class="hljs-params">(planet: PlanetTatooine)</span></span> { name = <span class="hljs-string">"Tatooine"</span> }
<span class="hljs-function"><span class="hljs-keyword">func</span> <span class="hljs-title">visit</span><span class="hljs-params">(planet: MoonJedha)</span></span> { name = <span class="hljs-string">"Jedha"</span> }
}
</code></pre>
<h3>Usage</h3>
<pre><code class="language-swift"><span class="hljs-keyword">let</span> planets: [<span class="hljs-type">Planet</span>] = [<span class="hljs-type">PlanetAlderaan</span>(), <span class="hljs-type">PlanetCoruscant</span>(), <span class="hljs-type">PlanetTatooine</span>(), <span class="hljs-type">MoonJedha</span>()]
<span class="hljs-keyword">let</span> names = planets.<span class="hljs-built_in">map</span> { (planet: <span class="hljs-type">Planet</span>) -> <span class="hljs-type">String</span> <span class="hljs-keyword">in</span>
<span class="hljs-keyword">let</span> visitor = <span class="hljs-type">NameVisitor</span>()
planet.accept(visitor: visitor)
<span class="hljs-keyword">return</span> visitor.name
}
names
</code></pre>
<h2>Creational</h2>
<blockquote>
<p>In software engineering, creational design patterns are design patterns that deal with object creation mechanisms, trying to create objects in a manner suitable to the situation. The basic form of object creation could result in design problems or added complexity to the design. Creational design patterns solve this problem by somehow controlling this object creation.</p>
<p><strong>Source:</strong> <a href="http://en.wikipedia.org/wiki/Creational_pattern">wikipedia.org</a></p>
</blockquote>
<h2>🌰 Abstract Factory</h2>
<p>The abstract factory pattern is used to provide a client with a set of related or dependant objects.
The “family” of objects created by the factory are determined at run-time.</p>
<h3>Example</h3>
<p>Protocols</p>
<pre><code class="language-swift"><span class="hljs-class"><span class="hljs-keyword">protocol</span> <span class="hljs-title">BurgerDescribing</span> </span>{
<span class="hljs-keyword">var</span> ingredients: [<span class="hljs-type">String</span>] { <span class="hljs-keyword">get</span> }
}
<span class="hljs-class"><span class="hljs-keyword">struct</span> <span class="hljs-title">CheeseBurger</span>: <span class="hljs-title">BurgerDescribing</span> </span>{
<span class="hljs-keyword">let</span> ingredients: [<span class="hljs-type">String</span>]
}
<span class="hljs-class"><span class="hljs-keyword">protocol</span> <span class="hljs-title">BurgerMaking</span> </span>{
<span class="hljs-function"><span class="hljs-keyword">func</span> <span class="hljs-title">make</span><span class="hljs-params">()</span></span> -> <span class="hljs-type">BurgerDescribing</span>
}
<span class="hljs-comment">// Number implementations with factory methods</span>
<span class="hljs-keyword">final</span> <span class="hljs-class"><span class="hljs-keyword">class</span> <span class="hljs-title">BigKahunaBurger</span>: <span class="hljs-title">BurgerMaking</span> </span>{
<span class="hljs-function"><span class="hljs-keyword">func</span> <span class="hljs-title">make</span><span class="hljs-params">()</span></span> -> <span class="hljs-type">BurgerDescribing</span> {
<span class="hljs-keyword">return</span> <span class="hljs-type">CheeseBurger</span>(ingredients: [<span class="hljs-string">"Cheese"</span>, <span class="hljs-string">"Burger"</span>, <span class="hljs-string">"Lettuce"</span>, <span class="hljs-string">"Tomato"</span>])
}
}
<span class="hljs-keyword">final</span> <span class="hljs-class"><span class="hljs-keyword">class</span> <span class="hljs-title">JackInTheBox</span>: <span class="hljs-title">BurgerMaking</span> </span>{
<span class="hljs-function"><span class="hljs-keyword">func</span> <span class="hljs-title">make</span><span class="hljs-params">()</span></span> -> <span class="hljs-type">BurgerDescribing</span> {
<span class="hljs-keyword">return</span> <span class="hljs-type">CheeseBurger</span>(ingredients: [<span class="hljs-string">"Cheese"</span>, <span class="hljs-string">"Burger"</span>, <span class="hljs-string">"Tomato"</span>, <span class="hljs-string">"Onions"</span>])
}
}
</code></pre>
<p>Abstract factory</p>
<pre><code class="language-swift">
<span class="hljs-class"><span class="hljs-keyword">enum</span> <span class="hljs-title">BurgerFactoryType</span>: <span class="hljs-title">BurgerMaking</span> </span>{
<span class="hljs-keyword">case</span> bigKahuna
<span class="hljs-keyword">case</span> jackInTheBox
<span class="hljs-function"><span class="hljs-keyword">func</span> <span class="hljs-title">make</span><span class="hljs-params">()</span></span> -> <span class="hljs-type">BurgerDescribing</span> {
<span class="hljs-keyword">switch</span> <span class="hljs-keyword">self</span> {
<span class="hljs-keyword">case</span> .bigKahuna:
<span class="hljs-keyword">return</span> <span class="hljs-type">BigKahunaBurger</span>().make()
<span class="hljs-keyword">case</span> .jackInTheBox:
<span class="hljs-keyword">return</span> <span class="hljs-type">JackInTheBox</span>().make()
}
}
}
</code></pre>
<h3>Usage</h3>
<pre><code class="language-swift"><span class="hljs-keyword">let</span> bigKahuna = <span class="hljs-type">BurgerFactoryType</span>.bigKahuna.make()
<span class="hljs-keyword">let</span> jackInTheBox = <span class="hljs-type">BurgerFactoryType</span>.jackInTheBox.make()
</code></pre>
<h2>👷 Builder</h2>
<p>The builder pattern is used to create complex objects with constituent parts that must be created in the same order or using a specific algorithm.
An external class controls the construction algorithm.</p>
<h3>Example</h3>
<pre><code class="language-swift"><span class="hljs-keyword">final</span> <span class="hljs-class"><span class="hljs-keyword">class</span> <span class="hljs-title">DeathStarBuilder</span> </span>{
<span class="hljs-keyword">var</span> x: <span class="hljs-type">Double</span>?
<span class="hljs-keyword">var</span> y: <span class="hljs-type">Double</span>?
<span class="hljs-keyword">var</span> z: <span class="hljs-type">Double</span>?
<span class="hljs-keyword">typealias</span> <span class="hljs-type">BuilderClosure</span> = (<span class="hljs-type">DeathStarBuilder</span>) -> ()
<span class="hljs-keyword">init</span>(buildClosure: <span class="hljs-type">BuilderClosure</span>) {
buildClosure(<span class="hljs-keyword">self</span>)
}
}
<span class="hljs-class"><span class="hljs-keyword">struct</span> <span class="hljs-title">DeathStar</span> : <span class="hljs-title">CustomStringConvertible</span> </span>{
<span class="hljs-keyword">let</span> x: <span class="hljs-type">Double</span>
<span class="hljs-keyword">let</span> y: <span class="hljs-type">Double</span>
<span class="hljs-keyword">let</span> z: <span class="hljs-type">Double</span>
<span class="hljs-keyword">init</span>?(builder: <span class="hljs-type">DeathStarBuilder</span>) {
<span class="hljs-keyword">if</span> <span class="hljs-keyword">let</span> x = builder.x, <span class="hljs-keyword">let</span> y = builder.y, <span class="hljs-keyword">let</span> z = builder.z {
<span class="hljs-keyword">self</span>.x = x
<span class="hljs-keyword">self</span>.y = y
<span class="hljs-keyword">self</span>.z = z
} <span class="hljs-keyword">else</span> {
<span class="hljs-keyword">return</span> <span class="hljs-literal">nil</span>
}
}
<span class="hljs-keyword">var</span> description:<span class="hljs-type">String</span> {
<span class="hljs-keyword">return</span> <span class="hljs-string">"Death Star at (x:\(x) y:\(y) z:\(z))"</span>
}
}
</code></pre>
<h3>Usage</h3>
<pre><code class="language-swift"><span class="hljs-keyword">let</span> empire = <span class="hljs-type">DeathStarBuilder</span> { builder <span class="hljs-keyword">in</span>
builder.x = <span class="hljs-number">0.1</span>
builder.y = <span class="hljs-number">0.2</span>
builder.z = <span class="hljs-number">0.3</span>
}
<span class="hljs-keyword">let</span> deathStar = <span class="hljs-type">DeathStar</span>(builder:empire)
</code></pre>
<h2>🏭 Factory Method</h2>
<p>The factory pattern is used to replace class constructors, abstracting the process of object generation so that the type of the object instantiated can be determined at run-time.</p>
<h3>Example</h3>
<pre><code class="language-swift"><span class="hljs-class"><span class="hljs-keyword">protocol</span> <span class="hljs-title">CurrencyDescribing</span> </span>{
<span class="hljs-keyword">var</span> symbol: <span class="hljs-type">String</span> { <span class="hljs-keyword">get</span> }
<span class="hljs-keyword">var</span> code: <span class="hljs-type">String</span> { <span class="hljs-keyword">get</span> }
}
<span class="hljs-keyword">final</span> <span class="hljs-class"><span class="hljs-keyword">class</span> <span class="hljs-title">Euro</span>: <span class="hljs-title">CurrencyDescribing</span> </span>{
<span class="hljs-keyword">var</span> symbol: <span class="hljs-type">String</span> { <span class="hljs-keyword">return</span> <span class="hljs-string">"€"</span> }
<span class="hljs-keyword">var</span> code: <span class="hljs-type">String</span> { <span class="hljs-keyword">return</span> <span class="hljs-string">"EUR"</span> }
}
<span class="hljs-keyword">final</span> <span class="hljs-class"><span class="hljs-keyword">class</span> <span class="hljs-title">UnitedStatesDolar</span>: <span class="hljs-title">CurrencyDescribing</span> </span>{
<span class="hljs-keyword">var</span> symbol: <span class="hljs-type">String</span> { <span class="hljs-keyword">return</span> <span class="hljs-string">"$"</span> }
<span class="hljs-keyword">var</span> code: <span class="hljs-type">String</span> { <span class="hljs-keyword">return</span> <span class="hljs-string">"USD"</span> }
}
<span class="hljs-class"><span class="hljs-keyword">enum</span> <span class="hljs-title">Country</span> </span>{
<span class="hljs-keyword">case</span> unitedStates
<span class="hljs-keyword">case</span> spain
<span class="hljs-keyword">case</span> uk
<span class="hljs-keyword">case</span> greece
}
<span class="hljs-class"><span class="hljs-keyword">enum</span> <span class="hljs-title">CurrencyFactory</span> </span>{
<span class="hljs-keyword">static</span> <span class="hljs-function"><span class="hljs-keyword">func</span> <span class="hljs-title">currency</span><span class="hljs-params">(<span class="hljs-keyword">for</span> country: Country)</span></span> -> <span class="hljs-type">CurrencyDescribing</span>? {
<span class="hljs-keyword">switch</span> country {
<span class="hljs-keyword">case</span> .spain, .greece:
<span class="hljs-keyword">return</span> <span class="hljs-type">Euro</span>()
<span class="hljs-keyword">case</span> .unitedStates:
<span class="hljs-keyword">return</span> <span class="hljs-type">UnitedStatesDolar</span>()
<span class="hljs-keyword">default</span>:
<span class="hljs-keyword">return</span> <span class="hljs-literal">nil</span>
}
}
}
</code></pre>
<h3>Usage</h3>
<pre><code class="language-swift"><span class="hljs-keyword">let</span> noCurrencyCode = <span class="hljs-string">"No Currency Code Available"</span>
<span class="hljs-type">CurrencyFactory</span>.currency(<span class="hljs-keyword">for</span>: .greece)?.code ?? noCurrencyCode
<span class="hljs-type">CurrencyFactory</span>.currency(<span class="hljs-keyword">for</span>: .spain)?.code ?? noCurrencyCode
<span class="hljs-type">CurrencyFactory</span>.currency(<span class="hljs-keyword">for</span>: .unitedStates)?.code ?? noCurrencyCode
<span class="hljs-type">CurrencyFactory</span>.currency(<span class="hljs-keyword">for</span>: .uk)?.code ?? noCurrencyCode
</code></pre>
<h2>🔂 Monostate</h2>
<p>The monostate pattern is another way to achieve singularity. It works through a completely different mechanism, it enforces the behavior of singularity without imposing structural constraints.
So in that case, monostate saves the state as static instead of the entire instance as a singleton.
<a href="http://staff.cs.utu.fi/~jounsmed/doos_06/material/SingletonAndMonostate.pdf">SINGLETON and MONOSTATE - Robert C. Martin</a></p>
<h3>Example:</h3>
<pre><code class="language-swift">
<span class="hljs-class"><span class="hljs-keyword">class</span> <span class="hljs-title">Settings</span> </span>{
<span class="hljs-class"><span class="hljs-keyword">enum</span> <span class="hljs-title">Theme</span> </span>{
<span class="hljs-keyword">case</span> `<span class="hljs-keyword">default</span>`
<span class="hljs-keyword">case</span> old
<span class="hljs-keyword">case</span> new
}
<span class="hljs-keyword">private</span> <span class="hljs-keyword">static</span> <span class="hljs-keyword">var</span> theme: <span class="hljs-type">Theme</span>?
<span class="hljs-keyword">var</span> currentTheme: <span class="hljs-type">Theme</span> {
<span class="hljs-keyword">get</span> { <span class="hljs-type">Settings</span>.theme ?? .<span class="hljs-keyword">default</span> }
<span class="hljs-keyword">set</span>(newTheme) { <span class="hljs-type">Settings</span>.theme = newTheme }
}
}
</code></pre>
<h3>Usage:</h3>
<pre><code class="language-swift"><span class="hljs-keyword">import</span> SwiftUI
<span class="hljs-comment">// When change the theme</span>
<span class="hljs-keyword">let</span> settings = <span class="hljs-type">Settings</span>() <span class="hljs-comment">// Starts using theme .old</span>
settings.currentTheme = .new <span class="hljs-comment">// Change theme to .new</span>
<span class="hljs-comment">// On screen 1</span>