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The Go
Programming
Language
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The Go
Programming
Language
Alan A. A. Donovan
Google Inc.
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Brian W. Kernighan
Princeton University
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The Go Programming Language
© 2016 Alan A. A. Donovan & Brian W. Kernighan
revision 3b600c, date 29 Sep 2015
Fo r Leil a an d Me g
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The Go Programming Language
© 2016 Alan A. A. Donovan & Brian W. Kernighan
revision 3b600c, date 29 Sep 2015
Cont ents
Pr eface xi
The Origins of Go xii
The Go Pro jec t xiii
Organizat ion of the Book xv ptg16091132
Wh ere to Find More Infor mat ion xvi
Ac knowledgments xvi
1. Tutorial 1
1.1. Hel lo, Wor ld 1
1.2. Comand-L ine Arguments 4
1.3. Finding Dup lic ate Lines 8
1.4. Animated GIFs 13
1.5. Fetching a URL 15
1.6. Fetching URLs Con cur rently 17
1.7. A We b Server 19
1.8. Loose End s 23
2. Pro gram Str ucture 27
2.1. Names 27
2.2. Declarat ions 28
2.3. Var iables 30
2.4. Asig nments 36
2.5. Typ e Decl arat ions 39
2.6. Packages and Files 41
2.7. Scope 45
vi
The Go Programming Language
© 2016 Alan A. A. Donovan & Brian W. Kernighan
revision 3b600c, date 29 Sep 2015
viii CONTENTS
3. Basic Data Typ es 51
3.1. Int egers 51
3.2. Float ing-Point Numbers 56
3.3. Complex Numbers 61
3.4. Boole ans 63
3.5. Str ings 64
3.6. Con stants 75
4. Com posite Typ es 81
4.1. Arays 81
4.2. Slices 84
4.3. Maps 93
4.4. Str ucts 99
4.5. JSON 107
4.6. Text and HTML Templ ates 113
5. Func tions 19
5.1. Function Declarat ions 19
5.2. Rec ursion 121
5.3. Multiple Retur n Values 124
5.4. Erro rs 127
5.5. Function Values 132
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5.6. Anony mou s Func tions 135
5.7. Var iadic Functions 142
5.8. Defer red Function Cal ls 143
5.9. Panic 148
5.10. Recov er 151
6. Metho ds 155
6.1. Met hod Declarat ions 15
6.2. Met hods wit h a Point er Receiver 158
6.3. Composing Typ es by Str uct Emb edding 161
6.4. Met hod Values and Expresions 164
6.5. Example: Bit Vec tor Typ e 165
6.6. Encapsulat ion 168
7. Interfaces 171
7.1. Int erfaces as Contrac ts 171
7.2. Int erface Typ es 174
7.3. Int erface Satisfac tion 175
7.4. Parsing Flags wit h flag.Value 179
7.5. Int erface Values 181
The Go Programming Language
© 2016 Alan A. A. Donovan & Brian W. Kernighan
revision 3b600c, date 29 Sep 2015
CONTENTS ix
7.6. Sor ting wit h sort.Interface 186
7.7. The htp.Handler Interface 191
7.8. The eror Interface 196
7.9. Example: Expression Evaluator 197
7.10. Typ e As ser tions 205
7.11. Discriminat ing Eror s with Typ e As ser tions 206
7.12. Quer ying Beh avior s with Int erface Typ e As ser tions 208
7.13. Typ e Sw itch es 210
7.14. Example: Token-B ased XML Decoding 213
7.15. A Fe w Wo rds of Adv ice 216
8. Gor o utines and Chanels 217
8.1. Goroutines 217
8.2. Example: Con cur rent Clo ck Ser ver 219
8.3. Example: Con cur rent Ech o Server 2
8.4. Channel s 225
8.5. Looping in Paral lel 234
8.6. Example: Con cur rent Web Craw ler 239
8.7. Multiplexing wit h select 244
8.8. Example: Con cur rent Direc tor y Traversal 247
8.9. Cancellat ion 251
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8.10. Example: Chat Ser ver 253
9. Concurrency with Shared Vari ables 257
9.1. Race Con dit ion s 257
9.2. Mut ual Exc lusion: sync.Mutex 262
9.3. Read/Write Mut exes: sync.RWMutex 266
9.4. Memor y Sy nchro nizat ion 267
9.5. Lazy Initializat ion: sync.Once 268
9.6. The Race Detec tor 271
9.7. Example: Con cur rent Non-Blo cking Cache 272
9.8. Goroutines and Threads 280
10. Pack ages and the Go Tool 283
10.1. Int roduc tion 283
10.2. Imp ort Pat hs 284
10.3. The Package Declarat ion 285
10.4. Imp ort Declarat ions 285
10.5. Blank Imp orts 286
10.6. Packages and Naming 289
10.7. The Go Tool 290
