-
Notifications
You must be signed in to change notification settings - Fork 78
/
MyFirstObjectWalk.html
1684 lines (1634 loc) · 71.8 KB
/
MyFirstObjectWalk.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 xmlns="http://www.w3.org/1999/xhtml" lang="en">
<head>
<meta charset="UTF-8"/>
<meta http-equiv="X-UA-Compatible" content="IE=edge"/>
<meta name="viewport" content="width=device-width, initial-scale=1.0"/>
<meta name="generator" content="Asciidoctor 2.0.20"/>
<title>My First Object Walk</title>
<link rel="stylesheet" href="https://fonts.googleapis.com/css?family=Open+Sans:300,300italic,400,400italic,600,600italic%7CNoto+Serif:400,400italic,700,700italic%7CDroid+Sans+Mono:400,700"/>
<style>
/*! Asciidoctor default stylesheet | MIT License | https://asciidoctor.org */
/* Uncomment the following line when using as a custom stylesheet */
/* @import "https://fonts.googleapis.com/css?family=Open+Sans:300,300italic,400,400italic,600,600italic%7CNoto+Serif:400,400italic,700,700italic%7CDroid+Sans+Mono:400,700"; */
html{font-family:sans-serif;-webkit-text-size-adjust:100%}
a{background:none}
a:focus{outline:thin dotted}
a:active,a:hover{outline:0}
h1{font-size:2em;margin:.67em 0}
b,strong{font-weight:bold}
abbr{font-size:.9em}
abbr[title]{cursor:help;border-bottom:1px dotted #dddddf;text-decoration:none}
dfn{font-style:italic}
hr{height:0}
mark{background:#ff0;color:#000}
code,kbd,pre,samp{font-family:monospace;font-size:1em}
pre{white-space:pre-wrap}
q{quotes:"\201C" "\201D" "\2018" "\2019"}
small{font-size:80%}
sub,sup{font-size:75%;line-height:0;position:relative;vertical-align:baseline}
sup{top:-.5em}
sub{bottom:-.25em}
img{border:0}
svg:not(:root){overflow:hidden}
figure{margin:0}
audio,video{display:inline-block}
audio:not([controls]){display:none;height:0}
fieldset{border:1px solid silver;margin:0 2px;padding:.35em .625em .75em}
legend{border:0;padding:0}
button,input,select,textarea{font-family:inherit;font-size:100%;margin:0}
button,input{line-height:normal}
button,select{text-transform:none}
button,html input[type=button],input[type=reset],input[type=submit]{-webkit-appearance:button;cursor:pointer}
button[disabled],html input[disabled]{cursor:default}
input[type=checkbox],input[type=radio]{padding:0}
button::-moz-focus-inner,input::-moz-focus-inner{border:0;padding:0}
textarea{overflow:auto;vertical-align:top}
table{border-collapse:collapse;border-spacing:0}
*,::before,::after{box-sizing:border-box}
html,body{font-size:100%}
body{background:#fff;color:rgba(0,0,0,.8);padding:0;margin:0;font-family:"Noto Serif","DejaVu Serif",serif;line-height:1;position:relative;cursor:auto;-moz-tab-size:4;-o-tab-size:4;tab-size:4;word-wrap:anywhere;-moz-osx-font-smoothing:grayscale;-webkit-font-smoothing:antialiased}
a:hover{cursor:pointer}
img,object,embed{max-width:100%;height:auto}
object,embed{height:100%}
img{-ms-interpolation-mode:bicubic}
.left{float:left!important}
.right{float:right!important}
.text-left{text-align:left!important}
.text-right{text-align:right!important}
.text-center{text-align:center!important}
.text-justify{text-align:justify!important}
.hide{display:none}
img,object,svg{display:inline-block;vertical-align:middle}
textarea{height:auto;min-height:50px}
select{width:100%}
.subheader,.admonitionblock td.content>.title,.audioblock>.title,.exampleblock>.title,.imageblock>.title,.listingblock>.title,.literalblock>.title,.stemblock>.title,.openblock>.title,.paragraph>.title,.quoteblock>.title,table.tableblock>.title,.verseblock>.title,.videoblock>.title,.dlist>.title,.olist>.title,.ulist>.title,.qlist>.title,.hdlist>.title{line-height:1.45;color:#7a2518;font-weight:400;margin-top:0;margin-bottom:.25em}
div,dl,dt,dd,ul,ol,li,h1,h2,h3,#toctitle,.sidebarblock>.content>.title,h4,h5,h6,pre,form,p,blockquote,th,td{margin:0;padding:0}
a{color:#2156a5;text-decoration:underline;line-height:inherit}
a:hover,a:focus{color:#1d4b8f}
a img{border:0}
p{line-height:1.6;margin-bottom:1.25em;text-rendering:optimizeLegibility}
p aside{font-size:.875em;line-height:1.35;font-style:italic}
h1,h2,h3,#toctitle,.sidebarblock>.content>.title,h4,h5,h6{font-family:"Open Sans","DejaVu Sans",sans-serif;font-weight:300;font-style:normal;color:#ba3925;text-rendering:optimizeLegibility;margin-top:1em;margin-bottom:.5em;line-height:1.0125em}
h1 small,h2 small,h3 small,#toctitle small,.sidebarblock>.content>.title small,h4 small,h5 small,h6 small{font-size:60%;color:#e99b8f;line-height:0}
h1{font-size:2.125em}
h2{font-size:1.6875em}
h3,#toctitle,.sidebarblock>.content>.title{font-size:1.375em}
h4,h5{font-size:1.125em}
h6{font-size:1em}
hr{border:solid #dddddf;border-width:1px 0 0;clear:both;margin:1.25em 0 1.1875em}
em,i{font-style:italic;line-height:inherit}
strong,b{font-weight:bold;line-height:inherit}
small{font-size:60%;line-height:inherit}
code{font-family:"Droid Sans Mono","DejaVu Sans Mono",monospace;font-weight:400;color:rgba(0,0,0,.9)}
ul,ol,dl{line-height:1.6;margin-bottom:1.25em;list-style-position:outside;font-family:inherit}
ul,ol{margin-left:1.5em}
ul li ul,ul li ol{margin-left:1.25em;margin-bottom:0}
ul.circle{list-style-type:circle}
ul.disc{list-style-type:disc}
ul.square{list-style-type:square}
ul.circle ul:not([class]),ul.disc ul:not([class]),ul.square ul:not([class]){list-style:inherit}
ol li ul,ol li ol{margin-left:1.25em;margin-bottom:0}
dl dt{margin-bottom:.3125em;font-weight:bold}
dl dd{margin-bottom:1.25em}
blockquote{margin:0 0 1.25em;padding:.5625em 1.25em 0 1.1875em;border-left:1px solid #ddd}
blockquote,blockquote p{line-height:1.6;color:rgba(0,0,0,.85)}
@media screen and (min-width:768px){h1,h2,h3,#toctitle,.sidebarblock>.content>.title,h4,h5,h6{line-height:1.2}
h1{font-size:2.75em}
h2{font-size:2.3125em}
h3,#toctitle,.sidebarblock>.content>.title{font-size:1.6875em}
h4{font-size:1.4375em}}
table{background:#fff;margin-bottom:1.25em;border:1px solid #dedede;word-wrap:normal}
table thead,table tfoot{background:#f7f8f7}
table thead tr th,table thead tr td,table tfoot tr th,table tfoot tr td{padding:.5em .625em .625em;font-size:inherit;color:rgba(0,0,0,.8);text-align:left}
table tr th,table tr td{padding:.5625em .625em;font-size:inherit;color:rgba(0,0,0,.8)}
table tr.even,table tr.alt{background:#f8f8f7}
table thead tr th,table tfoot tr th,table tbody tr td,table tr td,table tfoot tr td{line-height:1.6}
h1,h2,h3,#toctitle,.sidebarblock>.content>.title,h4,h5,h6{line-height:1.2;word-spacing:-.05em}
h1 strong,h2 strong,h3 strong,#toctitle strong,.sidebarblock>.content>.title strong,h4 strong,h5 strong,h6 strong{font-weight:400}
.center{margin-left:auto;margin-right:auto}
.stretch{width:100%}
.clearfix::before,.clearfix::after,.float-group::before,.float-group::after{content:" ";display:table}
.clearfix::after,.float-group::after{clear:both}
:not(pre).nobreak{word-wrap:normal}
:not(pre).nowrap{white-space:nowrap}
:not(pre).pre-wrap{white-space:pre-wrap}
:not(pre):not([class^=L])>code{font-size:.9375em;font-style:normal!important;letter-spacing:0;padding:.1em .5ex;word-spacing:-.15em;background:#f7f7f8;border-radius:4px;line-height:1.45;text-rendering:optimizeSpeed}
pre{color:rgba(0,0,0,.9);font-family:"Droid Sans Mono","DejaVu Sans Mono",monospace;line-height:1.45;text-rendering:optimizeSpeed}
pre code,pre pre{color:inherit;font-size:inherit;line-height:inherit}
pre>code{display:block}
pre.nowrap,pre.nowrap pre{white-space:pre;word-wrap:normal}
em em{font-style:normal}
strong strong{font-weight:400}
.keyseq{color:rgba(51,51,51,.8)}
kbd{font-family:"Droid Sans Mono","DejaVu Sans Mono",monospace;display:inline-block;color:rgba(0,0,0,.8);font-size:.65em;line-height:1.45;background:#f7f7f7;border:1px solid #ccc;border-radius:3px;box-shadow:0 1px 0 rgba(0,0,0,.2),inset 0 0 0 .1em #fff;margin:0 .15em;padding:.2em .5em;vertical-align:middle;position:relative;top:-.1em;white-space:nowrap}
.keyseq kbd:first-child{margin-left:0}
.keyseq kbd:last-child{margin-right:0}
.menuseq,.menuref{color:#000}
.menuseq b:not(.caret),.menuref{font-weight:inherit}
.menuseq{word-spacing:-.02em}
.menuseq b.caret{font-size:1.25em;line-height:.8}
.menuseq i.caret{font-weight:bold;text-align:center;width:.45em}
b.button::before,b.button::after{position:relative;top:-1px;font-weight:400}
b.button::before{content:"[";padding:0 3px 0 2px}
b.button::after{content:"]";padding:0 2px 0 3px}
p a>code:hover{color:rgba(0,0,0,.9)}
#header,#content,#footnotes,#footer{width:100%;margin:0 auto;max-width:62.5em;*zoom:1;position:relative;padding-left:.9375em;padding-right:.9375em}
#header::before,#header::after,#content::before,#content::after,#footnotes::before,#footnotes::after,#footer::before,#footer::after{content:" ";display:table}
#header::after,#content::after,#footnotes::after,#footer::after{clear:both}
#content{margin-top:1.25em}
#content::before{content:none}
#header>h1:first-child{color:rgba(0,0,0,.85);margin-top:2.25rem;margin-bottom:0}
#header>h1:first-child+#toc{margin-top:8px;border-top:1px solid #dddddf}
#header>h1:only-child,body.toc2 #header>h1:nth-last-child(2){border-bottom:1px solid #dddddf;padding-bottom:8px}
#header .details{border-bottom:1px solid #dddddf;line-height:1.45;padding-top:.25em;padding-bottom:.25em;padding-left:.25em;color:rgba(0,0,0,.6);display:flex;flex-flow:row wrap}
#header .details span:first-child{margin-left:-.125em}
#header .details span.email a{color:rgba(0,0,0,.85)}
#header .details br{display:none}
#header .details br+span::before{content:"\00a0\2013\00a0"}
#header .details br+span.author::before{content:"\00a0\22c5\00a0";color:rgba(0,0,0,.85)}
#header .details br+span#revremark::before{content:"\00a0|\00a0"}
#header #revnumber{text-transform:capitalize}
#header #revnumber::after{content:"\00a0"}
#content>h1:first-child:not([class]){color:rgba(0,0,0,.85);border-bottom:1px solid #dddddf;padding-bottom:8px;margin-top:0;padding-top:1rem;margin-bottom:1.25rem}
#toc{border-bottom:1px solid #e7e7e9;padding-bottom:.5em}
#toc>ul{margin-left:.125em}
#toc ul.sectlevel0>li>a{font-style:italic}
#toc ul.sectlevel0 ul.sectlevel1{margin:.5em 0}
#toc ul{font-family:"Open Sans","DejaVu Sans",sans-serif;list-style-type:none}
#toc li{line-height:1.3334;margin-top:.3334em}
#toc a{text-decoration:none}
#toc a:active{text-decoration:underline}
#toctitle{color:#7a2518;font-size:1.2em}
@media screen and (min-width:768px){#toctitle{font-size:1.375em}
body.toc2{padding-left:15em;padding-right:0}
#toc.toc2{margin-top:0!important;background:#f8f8f7;position:fixed;width:15em;left:0;top:0;border-right:1px solid #e7e7e9;border-top-width:0!important;border-bottom-width:0!important;z-index:1000;padding:1.25em 1em;height:100%;overflow:auto}
#toc.toc2 #toctitle{margin-top:0;margin-bottom:.8rem;font-size:1.2em}
#toc.toc2>ul{font-size:.9em;margin-bottom:0}
#toc.toc2 ul ul{margin-left:0;padding-left:1em}
#toc.toc2 ul.sectlevel0 ul.sectlevel1{padding-left:0;margin-top:.5em;margin-bottom:.5em}
body.toc2.toc-right{padding-left:0;padding-right:15em}
body.toc2.toc-right #toc.toc2{border-right-width:0;border-left:1px solid #e7e7e9;left:auto;right:0}}
@media screen and (min-width:1280px){body.toc2{padding-left:20em;padding-right:0}
#toc.toc2{width:20em}
#toc.toc2 #toctitle{font-size:1.375em}
#toc.toc2>ul{font-size:.95em}
#toc.toc2 ul ul{padding-left:1.25em}
body.toc2.toc-right{padding-left:0;padding-right:20em}}
#content #toc{border:1px solid #e0e0dc;margin-bottom:1.25em;padding:1.25em;background:#f8f8f7;border-radius:4px}
#content #toc>:first-child{margin-top:0}
#content #toc>:last-child{margin-bottom:0}
#footer{max-width:none;background:rgba(0,0,0,.8);padding:1.25em}
#footer-text{color:hsla(0,0%,100%,.8);line-height:1.44}
#content{margin-bottom:.625em}
.sect1{padding-bottom:.625em}
@media screen and (min-width:768px){#content{margin-bottom:1.25em}
.sect1{padding-bottom:1.25em}}
.sect1:last-child{padding-bottom:0}
.sect1+.sect1{border-top:1px solid #e7e7e9}
#content h1>a.anchor,h2>a.anchor,h3>a.anchor,#toctitle>a.anchor,.sidebarblock>.content>.title>a.anchor,h4>a.anchor,h5>a.anchor,h6>a.anchor{position:absolute;z-index:1001;width:1.5ex;margin-left:-1.5ex;display:block;text-decoration:none!important;visibility:hidden;text-align:center;font-weight:400}
#content h1>a.anchor::before,h2>a.anchor::before,h3>a.anchor::before,#toctitle>a.anchor::before,.sidebarblock>.content>.title>a.anchor::before,h4>a.anchor::before,h5>a.anchor::before,h6>a.anchor::before{content:"\00A7";font-size:.85em;display:block;padding-top:.1em}
#content h1:hover>a.anchor,#content h1>a.anchor:hover,h2:hover>a.anchor,h2>a.anchor:hover,h3:hover>a.anchor,#toctitle:hover>a.anchor,.sidebarblock>.content>.title:hover>a.anchor,h3>a.anchor:hover,#toctitle>a.anchor:hover,.sidebarblock>.content>.title>a.anchor:hover,h4:hover>a.anchor,h4>a.anchor:hover,h5:hover>a.anchor,h5>a.anchor:hover,h6:hover>a.anchor,h6>a.anchor:hover{visibility:visible}
#content h1>a.link,h2>a.link,h3>a.link,#toctitle>a.link,.sidebarblock>.content>.title>a.link,h4>a.link,h5>a.link,h6>a.link{color:#ba3925;text-decoration:none}
#content h1>a.link:hover,h2>a.link:hover,h3>a.link:hover,#toctitle>a.link:hover,.sidebarblock>.content>.title>a.link:hover,h4>a.link:hover,h5>a.link:hover,h6>a.link:hover{color:#a53221}
details,.audioblock,.imageblock,.literalblock,.listingblock,.stemblock,.videoblock{margin-bottom:1.25em}
details{margin-left:1.25rem}
details>summary{cursor:pointer;display:block;position:relative;line-height:1.6;margin-bottom:.625rem;outline:none;-webkit-tap-highlight-color:transparent}
details>summary::-webkit-details-marker{display:none}
details>summary::before{content:"";border:solid transparent;border-left:solid;border-width:.3em 0 .3em .5em;position:absolute;top:.5em;left:-1.25rem;transform:translateX(15%)}
details[open]>summary::before{border:solid transparent;border-top:solid;border-width:.5em .3em 0;transform:translateY(15%)}
details>summary::after{content:"";width:1.25rem;height:1em;position:absolute;top:.3em;left:-1.25rem}
.admonitionblock td.content>.title,.audioblock>.title,.exampleblock>.title,.imageblock>.title,.listingblock>.title,.literalblock>.title,.stemblock>.title,.openblock>.title,.paragraph>.title,.quoteblock>.title,table.tableblock>.title,.verseblock>.title,.videoblock>.title,.dlist>.title,.olist>.title,.ulist>.title,.qlist>.title,.hdlist>.title{text-rendering:optimizeLegibility;text-align:left;font-family:"Noto Serif","DejaVu Serif",serif;font-size:1rem;font-style:italic}
table.tableblock.fit-content>caption.title{white-space:nowrap;width:0}
.paragraph.lead>p,#preamble>.sectionbody>[class=paragraph]:first-of-type p{font-size:1.21875em;line-height:1.6;color:rgba(0,0,0,.85)}
.admonitionblock>table{border-collapse:separate;border:0;background:none;width:100%}
.admonitionblock>table td.icon{text-align:center;width:80px}
.admonitionblock>table td.icon img{max-width:none}
.admonitionblock>table td.icon .title{font-weight:bold;font-family:"Open Sans","DejaVu Sans",sans-serif;text-transform:uppercase}
.admonitionblock>table td.content{padding-left:1.125em;padding-right:1.25em;border-left:1px solid #dddddf;color:rgba(0,0,0,.6);word-wrap:anywhere}
.admonitionblock>table td.content>:last-child>:last-child{margin-bottom:0}
.exampleblock>.content{border:1px solid #e6e6e6;margin-bottom:1.25em;padding:1.25em;background:#fff;border-radius:4px}
.sidebarblock{border:1px solid #dbdbd6;margin-bottom:1.25em;padding:1.25em;background:#f3f3f2;border-radius:4px}
.sidebarblock>.content>.title{color:#7a2518;margin-top:0;text-align:center}
.exampleblock>.content>:first-child,.sidebarblock>.content>:first-child{margin-top:0}
.exampleblock>.content>:last-child,.exampleblock>.content>:last-child>:last-child,.exampleblock>.content .olist>ol>li:last-child>:last-child,.exampleblock>.content .ulist>ul>li:last-child>:last-child,.exampleblock>.content .qlist>ol>li:last-child>:last-child,.sidebarblock>.content>:last-child,.sidebarblock>.content>:last-child>:last-child,.sidebarblock>.content .olist>ol>li:last-child>:last-child,.sidebarblock>.content .ulist>ul>li:last-child>:last-child,.sidebarblock>.content .qlist>ol>li:last-child>:last-child{margin-bottom:0}
.literalblock pre,.listingblock>.content>pre{border-radius:4px;overflow-x:auto;padding:1em;font-size:.8125em}
@media screen and (min-width:768px){.literalblock pre,.listingblock>.content>pre{font-size:.90625em}}
@media screen and (min-width:1280px){.literalblock pre,.listingblock>.content>pre{font-size:1em}}
.literalblock pre,.listingblock>.content>pre:not(.highlight),.listingblock>.content>pre[class=highlight],.listingblock>.content>pre[class^="highlight "]{background:#f7f7f8}
.literalblock.output pre{color:#f7f7f8;background:rgba(0,0,0,.9)}
.listingblock>.content{position:relative}
.listingblock code[data-lang]::before{display:none;content:attr(data-lang);position:absolute;font-size:.75em;top:.425rem;right:.5rem;line-height:1;text-transform:uppercase;color:inherit;opacity:.5}
.listingblock:hover code[data-lang]::before{display:block}
.listingblock.terminal pre .command::before{content:attr(data-prompt);padding-right:.5em;color:inherit;opacity:.5}
.listingblock.terminal pre .command:not([data-prompt])::before{content:"$"}
.listingblock pre.highlightjs{padding:0}
.listingblock pre.highlightjs>code{padding:1em;border-radius:4px}
.listingblock pre.prettyprint{border-width:0}
.prettyprint{background:#f7f7f8}
pre.prettyprint .linenums{line-height:1.45;margin-left:2em}
pre.prettyprint li{background:none;list-style-type:inherit;padding-left:0}
pre.prettyprint li code[data-lang]::before{opacity:1}
pre.prettyprint li:not(:first-child) code[data-lang]::before{display:none}
table.linenotable{border-collapse:separate;border:0;margin-bottom:0;background:none}
table.linenotable td[class]{color:inherit;vertical-align:top;padding:0;line-height:inherit;white-space:normal}
table.linenotable td.code{padding-left:.75em}
table.linenotable td.linenos,pre.pygments .linenos{border-right:1px solid;opacity:.35;padding-right:.5em;-webkit-user-select:none;-moz-user-select:none;-ms-user-select:none;user-select:none}
pre.pygments span.linenos{display:inline-block;margin-right:.75em}
.quoteblock{margin:0 1em 1.25em 1.5em;display:table}
.quoteblock:not(.excerpt)>.title{margin-left:-1.5em;margin-bottom:.75em}
.quoteblock blockquote,.quoteblock p{color:rgba(0,0,0,.85);font-size:1.15rem;line-height:1.75;word-spacing:.1em;letter-spacing:0;font-style:italic;text-align:justify}
.quoteblock blockquote{margin:0;padding:0;border:0}
.quoteblock blockquote::before{content:"\201c";float:left;font-size:2.75em;font-weight:bold;line-height:.6em;margin-left:-.6em;color:#7a2518;text-shadow:0 1px 2px rgba(0,0,0,.1)}
.quoteblock blockquote>.paragraph:last-child p{margin-bottom:0}
.quoteblock .attribution{margin-top:.75em;margin-right:.5ex;text-align:right}
.verseblock{margin:0 1em 1.25em}
.verseblock pre{font-family:"Open Sans","DejaVu Sans",sans-serif;font-size:1.15rem;color:rgba(0,0,0,.85);font-weight:300;text-rendering:optimizeLegibility}
.verseblock pre strong{font-weight:400}
.verseblock .attribution{margin-top:1.25rem;margin-left:.5ex}
.quoteblock .attribution,.verseblock .attribution{font-size:.9375em;line-height:1.45;font-style:italic}
.quoteblock .attribution br,.verseblock .attribution br{display:none}
.quoteblock .attribution cite,.verseblock .attribution cite{display:block;letter-spacing:-.025em;color:rgba(0,0,0,.6)}
.quoteblock.abstract blockquote::before,.quoteblock.excerpt blockquote::before,.quoteblock .quoteblock blockquote::before{display:none}
.quoteblock.abstract blockquote,.quoteblock.abstract p,.quoteblock.excerpt blockquote,.quoteblock.excerpt p,.quoteblock .quoteblock blockquote,.quoteblock .quoteblock p{line-height:1.6;word-spacing:0}
.quoteblock.abstract{margin:0 1em 1.25em;display:block}
.quoteblock.abstract>.title{margin:0 0 .375em;font-size:1.15em;text-align:center}
.quoteblock.excerpt>blockquote,.quoteblock .quoteblock{padding:0 0 .25em 1em;border-left:.25em solid #dddddf}
.quoteblock.excerpt,.quoteblock .quoteblock{margin-left:0}
.quoteblock.excerpt blockquote,.quoteblock.excerpt p,.quoteblock .quoteblock blockquote,.quoteblock .quoteblock p{color:inherit;font-size:1.0625rem}
.quoteblock.excerpt .attribution,.quoteblock .quoteblock .attribution{color:inherit;font-size:.85rem;text-align:left;margin-right:0}
p.tableblock:last-child{margin-bottom:0}
td.tableblock>.content{margin-bottom:1.25em;word-wrap:anywhere}
td.tableblock>.content>:last-child{margin-bottom:-1.25em}
table.tableblock,th.tableblock,td.tableblock{border:0 solid #dedede}
table.grid-all>*>tr>*{border-width:1px}
table.grid-cols>*>tr>*{border-width:0 1px}
table.grid-rows>*>tr>*{border-width:1px 0}
table.frame-all{border-width:1px}
table.frame-ends{border-width:1px 0}
table.frame-sides{border-width:0 1px}
table.frame-none>colgroup+*>:first-child>*,table.frame-sides>colgroup+*>:first-child>*{border-top-width:0}
table.frame-none>:last-child>:last-child>*,table.frame-sides>:last-child>:last-child>*{border-bottom-width:0}
table.frame-none>*>tr>:first-child,table.frame-ends>*>tr>:first-child{border-left-width:0}
table.frame-none>*>tr>:last-child,table.frame-ends>*>tr>:last-child{border-right-width:0}
table.stripes-all>*>tr,table.stripes-odd>*>tr:nth-of-type(odd),table.stripes-even>*>tr:nth-of-type(even),table.stripes-hover>*>tr:hover{background:#f8f8f7}
th.halign-left,td.halign-left{text-align:left}
th.halign-right,td.halign-right{text-align:right}
th.halign-center,td.halign-center{text-align:center}
th.valign-top,td.valign-top{vertical-align:top}
th.valign-bottom,td.valign-bottom{vertical-align:bottom}
th.valign-middle,td.valign-middle{vertical-align:middle}
table thead th,table tfoot th{font-weight:bold}
tbody tr th{background:#f7f8f7}
tbody tr th,tbody tr th p,tfoot tr th,tfoot tr th p{color:rgba(0,0,0,.8);font-weight:bold}
p.tableblock>code:only-child{background:none;padding:0}
p.tableblock{font-size:1em}
ol{margin-left:1.75em}
ul li ol{margin-left:1.5em}
dl dd{margin-left:1.125em}
dl dd:last-child,dl dd:last-child>:last-child{margin-bottom:0}
li p,ul dd,ol dd,.olist .olist,.ulist .ulist,.ulist .olist,.olist .ulist{margin-bottom:.625em}
ul.checklist,ul.none,ol.none,ul.no-bullet,ol.no-bullet,ol.unnumbered,ul.unstyled,ol.unstyled{list-style-type:none}
ul.no-bullet,ol.no-bullet,ol.unnumbered{margin-left:.625em}
ul.unstyled,ol.unstyled{margin-left:0}
li>p:empty:only-child::before{content:"";display:inline-block}
ul.checklist>li>p:first-child{margin-left:-1em}
ul.checklist>li>p:first-child>.fa-square-o:first-child,ul.checklist>li>p:first-child>.fa-check-square-o:first-child{width:1.25em;font-size:.8em;position:relative;bottom:.125em}
ul.checklist>li>p:first-child>input[type=checkbox]:first-child{margin-right:.25em}
ul.inline{display:flex;flex-flow:row wrap;list-style:none;margin:0 0 .625em -1.25em}
ul.inline>li{margin-left:1.25em}
.unstyled dl dt{font-weight:400;font-style:normal}
ol.arabic{list-style-type:decimal}
ol.decimal{list-style-type:decimal-leading-zero}
ol.loweralpha{list-style-type:lower-alpha}
ol.upperalpha{list-style-type:upper-alpha}
ol.lowerroman{list-style-type:lower-roman}
ol.upperroman{list-style-type:upper-roman}
ol.lowergreek{list-style-type:lower-greek}
.hdlist>table,.colist>table{border:0;background:none}
.hdlist>table>tbody>tr,.colist>table>tbody>tr{background:none}
td.hdlist1,td.hdlist2{vertical-align:top;padding:0 .625em}
td.hdlist1{font-weight:bold;padding-bottom:1.25em}
td.hdlist2{word-wrap:anywhere}
.literalblock+.colist,.listingblock+.colist{margin-top:-.5em}
.colist td:not([class]):first-child{padding:.4em .75em 0;line-height:1;vertical-align:top}
.colist td:not([class]):first-child img{max-width:none}
.colist td:not([class]):last-child{padding:.25em 0}
.thumb,.th{line-height:0;display:inline-block;border:4px solid #fff;box-shadow:0 0 0 1px #ddd}
.imageblock.left{margin:.25em .625em 1.25em 0}
.imageblock.right{margin:.25em 0 1.25em .625em}
.imageblock>.title{margin-bottom:0}
.imageblock.thumb,.imageblock.th{border-width:6px}
.imageblock.thumb>.title,.imageblock.th>.title{padding:0 .125em}
.image.left,.image.right{margin-top:.25em;margin-bottom:.25em;display:inline-block;line-height:0}
.image.left{margin-right:.625em}
.image.right{margin-left:.625em}
a.image{text-decoration:none;display:inline-block}
a.image object{pointer-events:none}
sup.footnote,sup.footnoteref{font-size:.875em;position:static;vertical-align:super}
sup.footnote a,sup.footnoteref a{text-decoration:none}
sup.footnote a:active,sup.footnoteref a:active{text-decoration:underline}
#footnotes{padding-top:.75em;padding-bottom:.75em;margin-bottom:.625em}
#footnotes hr{width:20%;min-width:6.25em;margin:-.25em 0 .75em;border-width:1px 0 0}
#footnotes .footnote{padding:0 .375em 0 .225em;line-height:1.3334;font-size:.875em;margin-left:1.2em;margin-bottom:.2em}
#footnotes .footnote a:first-of-type{font-weight:bold;text-decoration:none;margin-left:-1.05em}
#footnotes .footnote:last-of-type{margin-bottom:0}
#content #footnotes{margin-top:-.625em;margin-bottom:0;padding:.75em 0}
div.unbreakable{page-break-inside:avoid}
.big{font-size:larger}
.small{font-size:smaller}
.underline{text-decoration:underline}
.overline{text-decoration:overline}
.line-through{text-decoration:line-through}
.aqua{color:#00bfbf}
.aqua-background{background:#00fafa}
.black{color:#000}
.black-background{background:#000}
.blue{color:#0000bf}
.blue-background{background:#0000fa}
.fuchsia{color:#bf00bf}
.fuchsia-background{background:#fa00fa}
.gray{color:#606060}
.gray-background{background:#7d7d7d}
.green{color:#006000}
.green-background{background:#007d00}
.lime{color:#00bf00}
.lime-background{background:#00fa00}
.maroon{color:#600000}
.maroon-background{background:#7d0000}
.navy{color:#000060}
.navy-background{background:#00007d}
.olive{color:#606000}
.olive-background{background:#7d7d00}
.purple{color:#600060}
.purple-background{background:#7d007d}
.red{color:#bf0000}
.red-background{background:#fa0000}
.silver{color:#909090}
.silver-background{background:#bcbcbc}
.teal{color:#006060}
.teal-background{background:#007d7d}
.white{color:#bfbfbf}
.white-background{background:#fafafa}
.yellow{color:#bfbf00}
.yellow-background{background:#fafa00}
span.icon>.fa{cursor:default}
a span.icon>.fa{cursor:inherit}
.admonitionblock td.icon [class^="fa icon-"]{font-size:2.5em;text-shadow:1px 1px 2px rgba(0,0,0,.5);cursor:default}
.admonitionblock td.icon .icon-note::before{content:"\f05a";color:#19407c}
.admonitionblock td.icon .icon-tip::before{content:"\f0eb";text-shadow:1px 1px 2px rgba(155,155,0,.8);color:#111}
.admonitionblock td.icon .icon-warning::before{content:"\f071";color:#bf6900}
.admonitionblock td.icon .icon-caution::before{content:"\f06d";color:#bf3400}
.admonitionblock td.icon .icon-important::before{content:"\f06a";color:#bf0000}
.conum[data-value]{display:inline-block;color:#fff!important;background:rgba(0,0,0,.8);border-radius:50%;text-align:center;font-size:.75em;width:1.67em;height:1.67em;line-height:1.67em;font-family:"Open Sans","DejaVu Sans",sans-serif;font-style:normal;font-weight:bold}
.conum[data-value] *{color:#fff!important}
.conum[data-value]+b{display:none}
.conum[data-value]::after{content:attr(data-value)}
pre .conum[data-value]{position:relative;top:-.125em}
b.conum *{color:inherit!important}
.conum:not([data-value]):empty{display:none}
dt,th.tableblock,td.content,div.footnote{text-rendering:optimizeLegibility}
h1,h2,p,td.content,span.alt,summary{letter-spacing:-.01em}
p strong,td.content strong,div.footnote strong{letter-spacing:-.005em}
p,blockquote,dt,td.content,td.hdlist1,span.alt,summary{font-size:1.0625rem}
p{margin-bottom:1.25rem}
.sidebarblock p,.sidebarblock dt,.sidebarblock td.content,p.tableblock{font-size:1em}
.exampleblock>.content{background:#fffef7;border-color:#e0e0dc;box-shadow:0 1px 4px #e0e0dc}
.print-only{display:none!important}
@page{margin:1.25cm .75cm}
@media print{*{box-shadow:none!important;text-shadow:none!important}
html{font-size:80%}
a{color:inherit!important;text-decoration:underline!important}
a.bare,a[href^="#"],a[href^="mailto:"]{text-decoration:none!important}
a[href^="http:"]:not(.bare)::after,a[href^="https:"]:not(.bare)::after{content:"(" attr(href) ")";display:inline-block;font-size:.875em;padding-left:.25em}
abbr[title]{border-bottom:1px dotted}
abbr[title]::after{content:" (" attr(title) ")"}
pre,blockquote,tr,img,object,svg{page-break-inside:avoid}
thead{display:table-header-group}
svg{max-width:100%}
p,blockquote,dt,td.content{font-size:1em;orphans:3;widows:3}
h2,h3,#toctitle,.sidebarblock>.content>.title{page-break-after:avoid}
#header,#content,#footnotes,#footer{max-width:none}
#toc,.sidebarblock,.exampleblock>.content{background:none!important}
#toc{border-bottom:1px solid #dddddf!important;padding-bottom:0!important}
body.book #header{text-align:center}
body.book #header>h1:first-child{border:0!important;margin:2.5em 0 1em}
body.book #header .details{border:0!important;display:block;padding:0!important}
body.book #header .details span:first-child{margin-left:0!important}
body.book #header .details br{display:block}
body.book #header .details br+span::before{content:none!important}
body.book #toc{border:0!important;text-align:left!important;padding:0!important;margin:0!important}
body.book #toc,body.book #preamble,body.book h1.sect0,body.book .sect1>h2{page-break-before:always}
.listingblock code[data-lang]::before{display:block}
#footer{padding:0 .9375em}
.hide-on-print{display:none!important}
.print-only{display:block!important}
.hide-for-print{display:none!important}
.show-for-print{display:inherit!important}}
@media amzn-kf8,print{#header>h1:first-child{margin-top:1.25rem}
.sect1{padding:0!important}
.sect1+.sect1{border:0}
#footer{background:none}
#footer-text{color:rgba(0,0,0,.6);font-size:.9em}}
@media amzn-kf8{#header,#content,#footnotes,#footer{padding:0}}
</style>
<style>
pre>code {
display: inline;
}
</style>
</head>
<body class="article">
<div id="header">
<h1>My First Object Walk</h1>
<div class="details">
<span id="revdate">2024-11-08</span>
</div>
</div>
<div id="content">
<div class="sect1">
<h2 id="_whats_an_object_walk">What’s an Object Walk?</h2>
<div class="sectionbody">
<div class="paragraph">
<p>The object walk is a key concept in Git - this is the process that underpins
operations like object transfer and fsck. Beginning from a given commit, the
list of objects is found by walking parent relationships between commits (commit
X based on commit W) and containment relationships between objects (tree Y is
contained within commit X, and blob Z is located within tree Y, giving our
working tree for commit X something like <code>y/z.txt</code>).</p>
</div>
<div class="paragraph">
<p>A related concept is the revision walk, which is focused on commit objects and
their parent relationships and does not delve into other object types. The
revision walk is used for operations like <code>git</code> <code>log</code>.</p>
</div>
<div class="sect2">
<h3 id="_related_reading">Related Reading</h3>
<div class="ulist">
<ul>
<li>
<p><code>Documentation/user-manual.txt</code> under "Hacking Git" contains some coverage of
the revision walker in its various incarnations.</p>
</li>
<li>
<p><code>revision.h</code></p>
</li>
<li>
<p><a href="https://eagain.net/articles/git-for-computer-scientists/">Git for Computer Scientists</a>
gives a good overview of the types of objects in Git and what your object
walk is really describing.</p>
</li>
</ul>
</div>
</div>
</div>
</div>
<div class="sect1">
<h2 id="_setting_up">Setting Up</h2>
<div class="sectionbody">
<div class="paragraph">
<p>Create a new branch from <code>master</code>.</p>
</div>
<div class="listingblock">
<div class="content">
<pre>git checkout -b revwalk origin/master</pre>
</div>
</div>
<div class="paragraph">
<p>We’ll put our fiddling into a new command. For fun, let’s name it <code>git</code> <code>walken</code>.
Open up a new file <code>builtin/walken.c</code> and set up the command handler:</p>
</div>
<div class="listingblock">
<div class="content">
<pre>/*
* "git walken"
*
* Part of the "My First Object Walk" tutorial.
*/
#include "builtin.h"
#include "trace.h"
int cmd_walken(int argc, const char **argv, const char *prefix)
{
trace_printf(_("cmd_walken incoming...\n"));
return 0;
}</pre>
</div>
</div>
<div class="admonitionblock note">
<table>
<tr>
<td class="icon">
<div class="title">Note</div>
</td>
<td class="content">
<code>trace_printf</code>(), defined in <code>trace.h</code>, differs from <code>printf</code>() in
that it can be turned on or off at runtime. For the purposes of this
tutorial, we will write <code>walken</code> as though it is intended for use as
a "plumbing" command: that is, a command which is used primarily in
scripts, rather than interactively by humans (a "porcelain" command).
So we will send our debug output to <code>trace_printf</code>() instead.
When running, enable trace output by setting the environment variable <code>GIT_TRACE</code>.
</td>
</tr>
</table>
</div>
<div class="paragraph">
<p>Add usage text and <code>-h</code> handling, like all subcommands should consistently do
(our test suite will notice and complain if you fail to do so).
We’ll need to include the <code>parse-options.h</code> header.</p>
</div>
<div class="listingblock">
<div class="content">
<pre>#include "parse-options.h"
...
int cmd_walken(int argc, const char **argv, const char *prefix)
{
const char * const walken_usage[] = {
N_("git walken"),
NULL,
};
struct option options[] = {
OPT_END()
};
argc = parse_options(argc, argv, prefix, options, walken_usage, 0);
...
}</pre>
</div>
</div>
<div class="paragraph">
<p>Also add the relevant line in <code>builtin.h</code> near <code>cmd_whatchanged</code>():</p>
</div>
<div class="listingblock">
<div class="content">
<pre>int cmd_walken(int argc, const char **argv, const char *prefix);</pre>
</div>
</div>
<div class="paragraph">
<p>Include the command in <code>git.c</code> in <code>commands</code>[] near the entry for <code>whatchanged</code>,
maintaining alphabetical ordering:</p>
</div>
<div class="listingblock">
<div class="content">
<pre>{ "walken", cmd_walken, RUN_SETUP },</pre>
</div>
</div>
<div class="paragraph">
<p>Add it to the <code>Makefile</code> near the line for <code>builtin/worktree.o</code>:</p>
</div>
<div class="listingblock">
<div class="content">
<pre>BUILTIN_OBJS += builtin/walken.o</pre>
</div>
</div>
<div class="paragraph">
<p>Build and test out your command, without forgetting to ensure the <code>DEVELOPER</code>
flag is set, and with <code>GIT_TRACE</code> enabled so the debug output can be seen:</p>
</div>
<div class="listingblock">
<div class="content">
<pre>$ echo DEVELOPER=1 >>config.mak
$ make
$ GIT_TRACE=1 ./bin-wrappers/git walken</pre>
</div>
</div>
<div class="admonitionblock note">
<table>
<tr>
<td class="icon">
<div class="title">Note</div>
</td>
<td class="content">
For a more exhaustive overview of the new command process, take a look at
<code>Documentation/MyFirstContribution.txt</code>.
</td>
</tr>
</table>
</div>
<div class="admonitionblock note">
<table>
<tr>
<td class="icon">
<div class="title">Note</div>
</td>
<td class="content">
A reference implementation can be found at
<a href="https://github.com/nasamuffin/git/tree/revwalk" class="bare">https://github.com/nasamuffin/git/tree/revwalk</a>.
</td>
</tr>
</table>
</div>
<div class="sect2">
<h3 id="_struct_rev_cmdline_info"><code>struct</code> <code>rev_cmdline_info</code></h3>
<div class="paragraph">
<p>The definition of <code>struct</code> <code>rev_cmdline_info</code> can be found in <code>revision.h</code>.</p>
</div>
<div class="paragraph">
<p>This struct is contained within the <code>rev_info</code> struct and is used to reflect
parameters provided by the user over the CLI.</p>
</div>
<div class="paragraph">
<p><code>nr</code> represents the number of <code>rev_cmdline_entry</code> present in the array.</p>
</div>
<div class="paragraph">
<p><code>alloc</code> is used by the <code>ALLOC_GROW</code> macro. Check <code>alloc.h</code> - this variable is
used to track the allocated size of the list.</p>
</div>
<div class="paragraph">
<p>Per entry, we find:</p>
</div>
<div class="paragraph">
<p><code>item</code> is the object provided upon which to base the object walk. Items in Git
can be blobs, trees, commits, or tags. (See <code>Documentation/gittutorial-2.txt</code>.)</p>
</div>
<div class="paragraph">
<p><code>name</code> is the object ID (OID) of the object - a hex string you may be familiar
with from using Git to organize your source in the past. Check the tutorial
mentioned above towards the top for a discussion of where the OID can come
from.</p>
</div>
<div class="paragraph">
<p><code>whence</code> indicates some information about what to do with the parents of the
specified object. We’ll explore this flag more later on; take a look at
<code>Documentation/revisions.txt</code> to get an idea of what could set the <code>whence</code>
value.</p>
</div>
<div class="paragraph">
<p><code>flags</code> are used to hint the beginning of the revision walk and are the first
block under the #include`s <code>in</code> `revision.<code>h</code>. The most likely ones to be set in
the <code>rev_cmdline_info</code> are <code>UNINTERESTING</code> and <code>BOTTOM</code>, but these same flags
can be used during the walk, as well.</p>
</div>
</div>
<div class="sect2">
<h3 id="_struct_rev_info"><code>struct</code> <code>rev_info</code></h3>
<div class="paragraph">
<p>This one is quite a bit longer, and many fields are only used during the walk
by <code>revision.c</code> - not configuration options. Most of the configurable flags in
<code>struct</code> <code>rev_info</code> have a mirror in <code>Documentation/rev-list-options.txt</code>. It’s a
good idea to take some time and read through that document.</p>
</div>
</div>
</div>
</div>
<div class="sect1">
<h2 id="_basic_commit_walk">Basic Commit Walk</h2>
<div class="sectionbody">
<div class="paragraph">
<p>First, let’s see if we can replicate the output of <code>git</code> <code>log</code> <code>--oneline</code>. We’ll
refer back to the implementation frequently to discover norms when performing
an object walk of our own.</p>
</div>
<div class="paragraph">
<p>To do so, we’ll first find all the commits, in order, which preceded the current
commit. We’ll extract the name and subject of the commit from each.</p>
</div>
<div class="paragraph">
<p>Ideally, we will also be able to find out which ones are currently at the tip of
various branches.</p>
</div>
<div class="sect2">
<h3 id="_setting_up_2">Setting Up</h3>
<div class="paragraph">
<p>Preparing for your object walk has some distinct stages.</p>
</div>
<div class="olist arabic">
<ol class="arabic">
<li>
<p>Perform default setup for this mode, and others which may be invoked.</p>
</li>
<li>
<p>Check configuration files for relevant settings.</p>
</li>
<li>
<p>Set up the <code>rev_info</code> struct.</p>
</li>
<li>
<p>Tweak the initialized <code>rev_info</code> to suit the current walk.</p>
</li>
<li>
<p>Prepare the <code>rev_info</code> for the walk.</p>
</li>
<li>
<p>Iterate over the objects, processing each one.</p>
</li>
</ol>
</div>
<div class="sect3">
<h4 id="_default_setups">Default Setups</h4>
<div class="paragraph">
<p>Before examining configuration files which may modify command behavior, set up
default state for switches or options your command may have. If your command
utilizes other Git components, ask them to set up their default states as well.
For instance, <code>git</code> <code>log</code> takes advantage of <code>grep</code> and <code>diff</code> functionality, so
its <code>init_log_defaults</code>() sets its own state (<code>decoration_style</code>) and asks
<code>grep</code> and <code>diff</code> to initialize themselves by calling each of their
initialization functions.</p>
</div>
</div>
<div class="sect3">
<h4 id="_configuring_from_gitconfig">Configuring From .<code>gitconfig</code></h4>
<div class="paragraph">
<p>Next, we should have a look at any relevant configuration settings (i.e.,
settings readable and settable from <code>git</code> <code>config</code>). This is done by providing a
callback to <code>git_config</code>(); within that callback, you can also invoke methods
from other components you may need that need to intercept these options. Your
callback will be invoked once per each configuration value which Git knows about
(global, local, worktree, etc.).</p>
</div>
<div class="paragraph">
<p>Similarly to the default values, we don’t have anything to do here yet
ourselves; however, we should call <code>git_default_config</code>() if we aren’t calling
any other existing config callbacks.</p>
</div>
<div class="paragraph">
<p>Add a new function to <code>builtin/walken.c</code>.
We’ll also need to include the <code>config.h</code> header:</p>
</div>
<div class="listingblock">
<div class="content">
<pre>#include "config.h"
...
static int git_walken_config(const char *var, const char *value,
const struct config_context *ctx, void *cb)
{
/*
* For now, we don't have any custom configuration, so fall back to
* the default config.
*/
return git_default_config(var, value, ctx, cb);
}</pre>
</div>
</div>
<div class="paragraph">
<p>Make sure to invoke <code>git_config</code>() with it in your <code>cmd_walken</code>():</p>
</div>
<div class="listingblock">
<div class="content">
<pre>int cmd_walken(int argc, const char **argv, const char *prefix)
{
...
git_config(git_walken_config, NULL);
...
}</pre>
</div>
</div>
</div>
<div class="sect3">
<h4 id="_setting_up_rev_info">Setting Up <code>rev_info</code></h4>
<div class="paragraph">
<p>Now that we’ve gathered external configuration and options, it’s time to
initialize the <code>rev_info</code> object which we will use to perform the walk. This is
typically done by calling <code>repo_init_revisions</code>() with the repository you intend
to target, as well as the <code>prefix</code> argument of <code>cmd_walken</code> and your <code>rev_info</code>
struct.</p>
</div>
<div class="paragraph">
<p>Add the <code>struct</code> <code>rev_info</code> and the <code>repo_init_revisions</code>() call.
We’ll also need to include the <code>revision.h</code> header:</p>
</div>
<div class="listingblock">
<div class="content">
<pre>#include "revision.h"
...
int cmd_walken(int argc, const char **argv, const char *prefix)
{
/* This can go wherever you like in your declarations.*/
struct rev_info rev;
...
/* This should go after the git_config() call. */
repo_init_revisions(the_repository, &rev, prefix);
...
}</pre>
</div>
</div>
</div>
<div class="sect3">
<h4 id="_tweaking_rev_info_for_the_walk">Tweaking <code>rev_info</code> For the Walk</h4>
<div class="paragraph">
<p>We’re getting close, but we’re still not quite ready to go. Now that <code>rev</code> is
initialized, we can modify it to fit our needs. This is usually done within a
helper for clarity, so let’s add one:</p>
</div>
<div class="listingblock">
<div class="content">
<pre>static void final_rev_info_setup(struct rev_info *rev)
{
/*
* We want to mimic the appearance of `git log --oneline`, so let's
* force oneline format.
*/
get_commit_format("oneline", rev);
/* Start our object walk at HEAD. */
add_head_to_pending(rev);
}</pre>
</div>
</div>
<div class="admonitionblock note">
<table>
<tr>
<td class="icon">
<div class="title">Note</div>
</td>
<td class="content">
<div class="paragraph">
<p>Instead of using the shorthand <code>add_head_to_pending</code>(), you could do
something like this:</p>
</div>
<div class="listingblock">
<div class="content">
<pre> struct setup_revision_opt opt;
memset(&opt, 0, sizeof(opt));
opt.def = "HEAD";
opt.revarg_opt = REVARG_COMMITTISH;
setup_revisions(argc, argv, rev, &opt);</pre>
</div>
</div>
<div class="paragraph">
<p>Using a <code>setup_revision_opt</code> gives you finer control over your walk’s starting
point.</p>
</div>
</td>
</tr>
</table>
</div>
<div class="paragraph">
<p>Then let’s invoke <code>final_rev_info_setup</code>() after the call to
<code>repo_init_revisions</code>():</p>
</div>
<div class="listingblock">
<div class="content">
<pre>int cmd_walken(int argc, const char **argv, const char *prefix)
{
...
final_rev_info_setup(&rev);
...
}</pre>
</div>
</div>
<div class="paragraph">
<p>Later, we may wish to add more arguments to <code>final_rev_info_setup</code>(). But for
now, this is all we need.</p>
</div>
</div>
<div class="sect3">
<h4 id="_preparing_rev_info_for_the_walk">Preparing <code>rev_info</code> For the Walk</h4>
<div class="paragraph">
<p>Now that <code>rev</code> is all initialized and configured, we’ve got one more setup step
before we get rolling. We can do this in a helper, which will both prepare the
<code>rev_info</code> for the walk, and perform the walk itself. Let’s start the helper
with the call to <code>prepare_revision_walk</code>(), which can return an error without
dying on its own:</p>
</div>
<div class="listingblock">
<div class="content">
<pre>static void walken_commit_walk(struct rev_info *rev)
{
if (prepare_revision_walk(rev))
die(_("revision walk setup failed"));
}</pre>
</div>
</div>
<div class="admonitionblock note">
<table>
<tr>
<td class="icon">
<div class="title">Note</div>
</td>
<td class="content">
<code>die</code>() prints to <code>stderr</code> and exits the program. Since it will print to
<code>stderr</code> it’s likely to be seen by a human, so we will localize it.
</td>
</tr>
</table>
</div>
</div>
<div class="sect3">
<h4 id="_performing_the_walk">Performing the Walk!</h4>
<div class="paragraph">
<p>Finally! We are ready to begin the walk itself. Now we can see that <code>rev_info</code>
can also be used as an iterator; we move to the next item in the walk by using
<code>get_revision</code>() repeatedly. Add the listed variable declarations at the top and
the walk loop below the <code>prepare_revision_walk</code>() call within your
<code>walken_commit_walk</code>():</p>
</div>
<div class="listingblock">
<div class="content">
<pre>#include "pretty.h"
...
static void walken_commit_walk(struct rev_info *rev)
{
struct commit *commit;
struct strbuf prettybuf = STRBUF_INIT;
...
while ((commit = get_revision(rev))) {
strbuf_reset(&prettybuf);
pp_commit_easy(CMIT_FMT_ONELINE, commit, &prettybuf);
puts(prettybuf.buf);
}
strbuf_release(&prettybuf);
}</pre>
</div>
</div>
<div class="admonitionblock note">
<table>
<tr>
<td class="icon">
<div class="title">Note</div>
</td>
<td class="content">
<code>puts</code>() prints a <code>char</code>* to <code>stdout</code>. Since this is the part of the
command we expect to be machine-parsed, we’re sending it directly to stdout.
</td>
</tr>
</table>
</div>
<div class="paragraph">
<p>Give it a shot.</p>
</div>
<div class="listingblock">
<div class="content">
<pre>$ make
$ ./bin-wrappers/git walken</pre>
</div>
</div>
<div class="paragraph">
<p>You should see all of the subject lines of all the commits in
your tree’s history, in order, ending with the initial commit, "Initial revision
of "git", the information manager from hell". Congratulations! You’ve written
your first revision walk. You can play with printing some additional fields
from each commit if you’re curious; have a look at the functions available in
<code>commit.h</code>.</p>
</div>
</div>
</div>
<div class="sect2">
<h3 id="_adding_a_filter">Adding a Filter</h3>
<div class="paragraph">
<p>Next, let’s try to filter the commits we see based on their author. This is
equivalent to running <code>git</code> <code>log</code> <code>--author=</code><em><pattern></em>. We can add a filter by
modifying <code>rev_info.grep_filter</code>, which is a <code>struct</code> <code>grep_opt</code>.</p>
</div>
<div class="paragraph">
<p>First some setup. Add <code>grep_config</code>() to <code>git_walken_config</code>():</p>
</div>
<div class="listingblock">
<div class="content">
<pre>static int git_walken_config(const char *var, const char *value,
const struct config_context *ctx, void *cb)
{