Programming in Scala: A Comprehensive Step-by-step Guide

754 Pages·2008·2.466 MB·English

by  Odersky M., Spoon L., Venners B.

Cover·Overview·Contents·Discuss·Suggest·Glossary·Index
Programming in Scala
Cover·Overview·Contents·Discuss·Suggest·Glossary·Index
Programming in Scala
Martin Odersky, Lex Spoon, Bill Venners
artima
ARTIMAPRESS
MOUNTAINVIEW,CALIFORNIA
Cover·Overview·Contents·Discuss·Suggest·Glossary·Index
iv
ProgramminginScala
FirstEdition,Version6
MartinOderskyisthecreatoroftheScalalanguageandaprofessoratEPFLin
Lausanne,Switzerland. LexSpoonworkedonScalafortwoyearsasapost-doc
withMartinOdersky. BillVennersispresidentofArtima,Inc.
ArtimaPressisanimprintofArtima,Inc.
P.O.Box390122,MountainView,California94039
Copyright©2007,2008MartinOdersky,LexSpoon,andBillVenners.
Allrightsreserved.
FirsteditionpublishedasPrePrint™eBook2007
Firsteditionpublished2008
ProducedintheUnitedStatesofAmerica
1211100908 56789
ISBN-10: 0-9815316-1-X
ISBN-13: 978-0-9815316-1-8
Nopartofthispublicationmaybereproduced,modified,distributed,storedina
retrievalsystem,republished,displayed,orperformed,forcommercialor
noncommercialpurposesorforcompensationofanykindwithoutpriorwritten
permissionfromArtima,Inc.
Allinformationandmaterialsinthisbookareprovided"asis"andwithout
warrantyofanykind.
Theterm“Artima”andtheArtimalogoaretrademarksorregisteredtrademarksof
Artima,Inc. Allothercompanyand/orproductnamesmaybetrademarksor
registeredtrademarksoftheirowners.
Cover·Overview·Contents·Discuss·Suggest·Glossary·Index
toNastaran-M.O.
toFay-L.S.
toSiew-B.V.
Cover·Overview·Contents·Discuss·Suggest·Glossary·Index
Overview
Contents vii
ListofFigures xvii
ListofTables xix
ListofListings xx
Foreword xxvii
Acknowledgments xxix
Introduction xxxi
1. AScalableLanguage 39
2. FirstStepsinScala 58
3. NextStepsinScala 71
4. ClassesandObjects 93
5. BasicTypesandOperations 107
6. FunctionalObjects 129
7. Built-inControlStructures 149
8. FunctionsandClosures 173
9. ControlAbstraction 194
10. CompositionandInheritance 209
11. Scala’sHierarchy 237
12. Traits 245
13. PackagesandImports 264
14. AssertionsandUnitTesting 279
15. CaseClassesandPatternMatching 293
16. WorkingwithLists 327
17. Collections 359
18. StatefulObjects 387
19. TypeParameterization 410
20. AbstractMembers 435
21. ImplicitConversionsandParameters 465
22. ImplementingLists 487
23. ForExpressionsRevisited 500
24. Extractors 516
25. Annotations 532
26. WorkingwithXML 539
27. ModularProgrammingUsingObjects 553
28. ObjectEquality 568
29. CombiningScalaandJava 594
30. ActorsandConcurrency 607
31. CombinatorParsing 642
32. GUIProgramming 671
33. TheSCellsSpreadsheet 683
A. ScalascriptsonUnixandWindows 708
Glossary 709
Bibliography 725
AbouttheAuthors 728
Index 729
Cover·Overview·Contents·Discuss·Suggest·Glossary·Index
Contents
Contents vii
ListofFigures xvii
ListofTables xix
ListofListings xx
Foreword xxvii
Acknowledgments xxix
Introduction xxxi
1 AScalableLanguage 39
1.1 Alanguagethatgrowsonyou . . . . . . . . . . . . . . 40
1.2 WhatmakesScalascalable? . . . . . . . . . . . . . . . 45
1.3 WhyScala?. . . . . . . . . . . . . . . . . . . . . . . . 48
1.4 Scala’sroots . . . . . . . . . . . . . . . . . . . . . . . 55
1.5 Conclusion . . . . . . . . . . . . . . . . . . . . . . . . 57
2 FirstStepsinScala 58
Step1. LearntousetheScalainterpreter . . . . . . . . . . . . 58
Step2. Definesomevariables . . . . . . . . . . . . . . . . . 60
Step3. Definesomefunctions . . . . . . . . . . . . . . . . . 62
Step4. WritesomeScalascripts . . . . . . . . . . . . . . . . 64
Step5. Loopwithwhile;decidewithif . . . . . . . . . . . 65
Step6. Iteratewithforeachandfor . . . . . . . . . . . . . 67
Conclusion . . . . . . . . . . . . . . . . . . . . . . . . . . . 70
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Contents viii
3 NextStepsinScala 71
Step7. Parameterizearrayswithtypes . . . . . . . . . . . . 71
Step8. Uselists . . . . . . . . . . . . . . . . . . . . . . . . 75
Step9. Usetuples . . . . . . . . . . . . . . . . . . . . . . . 80
Step10. Usesetsandmaps . . . . . . . . . . . . . . . . . . . 81
Step11. Learntorecognizethefunctionalstyle . . . . . . . . 86
Step12. Readlinesfromafile . . . . . . . . . . . . . . . . . 89
Conclusion . . . . . . . . . . . . . . . . . . . . . . . . . . . 92
4 ClassesandObjects 93
4.1 Classes,fields,andmethods . . . . . . . . . . . . . . . 93
4.2 Semicoloninference . . . . . . . . . . . . . . . . . . . 98
4.3 Singletonobjects . . . . . . . . . . . . . . . . . . . . . 99
4.4 AScalaapplication . . . . . . . . . . . . . . . . . . . 102
4.5 TheApplicationtrait . . . . . . . . . . . . . . . . . . 105
4.6 Conclusion . . . . . . . . . . . . . . . . . . . . . . . . 106
5 BasicTypesandOperations 107
5.1 Somebasictypes . . . . . . . . . . . . . . . . . . . . . 107
5.2 Literals . . . . . . . . . . . . . . . . . . . . . . . . . . 108
5.3 Operatorsaremethods . . . . . . . . . . . . . . . . . . 115
5.4 Arithmeticoperations . . . . . . . . . . . . . . . . . . 118
5.5 Relationalandlogicaloperations . . . . . . . . . . . . 119
5.6 Bitwiseoperations . . . . . . . . . . . . . . . . . . . . 121
5.7 Objectequality . . . . . . . . . . . . . . . . . . . . . . 123
5.8 Operatorprecedenceandassociativity . . . . . . . . . . 124
5.9 Richwrappers . . . . . . . . . . . . . . . . . . . . . . 127
5.10 Conclusion . . . . . . . . . . . . . . . . . . . . . . . . 127
6 FunctionalObjects 129
6.1 AspecificationforclassRational . . . . . . . . . . . 129
6.2 ConstructingaRational . . . . . . . . . . . . . . . . 130
6.3 ReimplementingthetoStringmethod . . . . . . . . . 132
6.4 Checkingpreconditions . . . . . . . . . . . . . . . . . 133
6.5 Addingfields . . . . . . . . . . . . . . . . . . . . . . . 133
6.6 Selfreferences . . . . . . . . . . . . . . . . . . . . . . 135
6.7 Auxiliaryconstructors . . . . . . . . . . . . . . . . . . 136
6.8 Privatefieldsandmethods . . . . . . . . . . . . . . . . 138
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Contents ix
6.9 Definingoperators . . . . . . . . . . . . . . . . . . . . 139
6.10 IdentifiersinScala . . . . . . . . . . . . . . . . . . . . 141
6.11 Methodoverloading . . . . . . . . . . . . . . . . . . . 144
6.12 Implicitconversions . . . . . . . . . . . . . . . . . . . 146
6.13 Awordofcaution . . . . . . . . . . . . . . . . . . . . 147
6.14 Conclusion . . . . . . . . . . . . . . . . . . . . . . . . 147
7 Built-inControlStructures 149
7.1 Ifexpressions . . . . . . . . . . . . . . . . . . . . . . 150
7.2 Whileloops . . . . . . . . . . . . . . . . . . . . . . . 151
7.3 Forexpressions . . . . . . . . . . . . . . . . . . . . . . 154
7.4 Exceptionhandlingwithtryexpressions . . . . . . . . 159
7.5 Matchexpressions . . . . . . . . . . . . . . . . . . . . 163
7.6 Livingwithoutbreakandcontinue . . . . . . . . . . 165
7.7 Variablescope . . . . . . . . . . . . . . . . . . . . . . 167
7.8 Refactoringimperative-stylecode . . . . . . . . . . . . 170
7.9 Conclusion . . . . . . . . . . . . . . . . . . . . . . . . 172
8 FunctionsandClosures 173
8.1 Methods . . . . . . . . . . . . . . . . . . . . . . . . . 173
8.2 Localfunctions . . . . . . . . . . . . . . . . . . . . . . 175
8.3 First-classfunctions . . . . . . . . . . . . . . . . . . . 177
8.4 Shortformsoffunctionliterals . . . . . . . . . . . . . 179
8.5 Placeholdersyntax . . . . . . . . . . . . . . . . . . . . 180
8.6 Partiallyappliedfunctions . . . . . . . . . . . . . . . . 181
8.7 Closures . . . . . . . . . . . . . . . . . . . . . . . . . 184
8.8 Repeatedparameters . . . . . . . . . . . . . . . . . . . 188
8.9 Tailrecursion . . . . . . . . . . . . . . . . . . . . . . . 189
8.10 Conclusion . . . . . . . . . . . . . . . . . . . . . . . . 193
9 ControlAbstraction 194
9.1 Reducingcodeduplication . . . . . . . . . . . . . . . . 194
9.2 Simplifyingclientcode . . . . . . . . . . . . . . . . . 198
9.3 Currying . . . . . . . . . . . . . . . . . . . . . . . . . 200
9.4 Writingnewcontrolstructures . . . . . . . . . . . . . . 202
9.5 By-nameparameters . . . . . . . . . . . . . . . . . . . 205
9.6 Conclusion . . . . . . . . . . . . . . . . . . . . . . . . 208
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10 CompositionandInheritance 209
10.1 Atwo-dimensionallayoutlibrary . . . . . . . . . . . . 209
10.2 Abstractclasses . . . . . . . . . . . . . . . . . . . . . 210
10.3 Definingparameterlessmethods . . . . . . . . . . . . . 211
10.4 Extendingclasses . . . . . . . . . . . . . . . . . . . . 214
10.5 Overridingmethodsandfields . . . . . . . . . . . . . . 216
10.6 Definingparametricfields . . . . . . . . . . . . . . . . 217
10.7 Invokingsuperclassconstructors. . . . . . . . . . . . . 219
10.8 Usingoverridemodifiers . . . . . . . . . . . . . . . . 220
10.9 Polymorphismanddynamicbinding . . . . . . . . . . 222
10.10 Declaringfinalmembers . . . . . . . . . . . . . . . . . 224
10.11 Usingcompositionandinheritance . . . . . . . . . . . 226
10.12 Implementingabove,beside,andtoString . . . . . . 227
10.13 Definingafactoryobject . . . . . . . . . . . . . . . . . 229
10.14 Heightenandwiden . . . . . . . . . . . . . . . . . . . 231
10.15 Puttingitalltogether . . . . . . . . . . . . . . . . . . . 235
10.16 Conclusion . . . . . . . . . . . . . . . . . . . . . . . . 236
11 Scala’sHierarchy 237
11.1 Scala’sclasshierarchy . . . . . . . . . . . . . . . . . . 237
11.2 Howprimitivesareimplemented . . . . . . . . . . . . 241
11.3 Bottomtypes . . . . . . . . . . . . . . . . . . . . . . . 243
11.4 Conclusion . . . . . . . . . . . . . . . . . . . . . . . . 244
12 Traits 245
12.1 Howtraitswork . . . . . . . . . . . . . . . . . . . . . 245
12.2 Thinversusrichinterfaces . . . . . . . . . . . . . . . . 248
12.3 Example: Rectangularobjects . . . . . . . . . . . . . . 249
12.4 TheOrderedtrait . . . . . . . . . . . . . . . . . . . . 252
12.5 Traitsasstackablemodifications. . . . . . . . . . . . . 254
12.6 Whynotmultipleinheritance? . . . . . . . . . . . . . . 258
12.7 Totrait,ornottotrait? . . . . . . . . . . . . . . . . . . 262
12.8 Conclusion . . . . . . . . . . . . . . . . . . . . . . . . 263
13 PackagesandImports 264
13.1 Packages . . . . . . . . . . . . . . . . . . . . . . . . . 264
13.2 Imports . . . . . . . . . . . . . . . . . . . . . . . . . . 268
13.3 Implicitimports . . . . . . . . . . . . . . . . . . . . . 272
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