Programming in Ada 2012 Programming in Ada 2012 JOHN BARNES UniversityPrintingHouse,CambridgeCB28BS,UnitedKingdom CambridgeUniversityPressispartoftheUniversityofCambridge. ItfurtherstheUniversity’smissionbydisseminatingknowledgeinthepursuitof education,learningandresearchatthehighestinternationallevelsofexcellence. www.cambridge.org Informationonthistitle:www.cambridge.org/9781107424814 ©JohnBarnes2014 Thispublicationisincopyright.Subjecttostatutoryexception andtotheprovisionsofrelevantcollectivelicensingagreements, noreproductionofanypartmaytakeplacewithoutthewritten permissionofCambridgeUniversityPress. 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To Barbara Contents Foreword xv Preface xix Part 1 An Overview 1 1 Introduction 3 1.1 Standard development 3 1.2 Software engineering 4 1.3 Evolution and abstraction 6 1.4 Structure and objectives of this book 8 1.5 References 10 2 Simple Concepts 11 2.1 Key goals 11 2.2 Overall structure 12 2.3 The scalar type model 17 2.4 Arrays and records 19 2.5 Access types 22 2.6 Errors and exceptions 23 2.7 Terminology 26 3 Abstraction 27 3.1 Packages and private types 27 3.2 Objects and inheritance 30 3.3 Classes and polymorphism 34 3.4 Genericity 40 3.5 Object oriented terminology 41 3.6 Tasking 43 4 Programs and Libraries 47 4.1 The hierarchical library 47 4.2 Input–output 49 vii viii Contents 4.3 Numeric library 52 4.4 Running a program 54 Program 1 Magic Moments 59 Part 2 Algorithmic Aspects 63 5 Lexical Style 65 5.1 Syntax notation 65 5.2 Lexical elements 66 5.3 Identifiers 67 5.4 Numbers 68 5.5 Comments 71 5.6 Pragmas and aspects 71 6 Scalar Types 73 6.1 Object declarations and assignments 73 6.2 Blocks and scopes 75 6.3 Types 77 6.4 Subtypes 79 6.5 Simple numeric types 81 6.6 Enumeration types 87 6.7 The type Boolean 90 6.8 Categories of types 93 6.9 Expression summary 95 7 Control Structures 101 7.1 If statements 101 7.2 Case statements 105 7.3 Loop statements 108 7.4 Goto statements and labels 114 7.5 Statement classification 111 8 Arrays and Records 117 8.1 Arrays 117 8.2 Array types 122 8.3 Array aggregates 127 8.4 Characters and strings 132 8.5 Arrays of arrays and slices 135 8.6 One-dimensional array operations 138 8.7 Records 143 9 Expression structures 149 9.1 Membership tests 149 9.2 If expressions 151 9.3 Case expressions 155 Contents ix 9.4 Quantified expressions 157 10 Subprograms 161 10.1 Functions 161 10.2 Operators 169 10.3 Procedures 171 10.4 Aliasing 177 10.5 Named and default parameters 179 10.6 Overloading 181 10.7 Declarations, scopes and visibility 182 11 Access Types 189 11.1 Flexibility versus integrity 189 11.2 Access types and allocators 191 11.3 Null exclusion and constraints 198 11.4 Aliased objects 200 11.5 Accessibility 204 11.6 Access parameters 206 11.7 Anonymous access types 210 11.8 Access to subprograms 214 11.9 Storage pools 220 Program 2 Sylvan Sorter 223 Part 3 The Big Picture 227 12 Packages and Private Types 229 12.1 Packages 229 12.2 Private types 234 12.3 Primitive operations and derived types 241 12.4 Equality 247 12.5 Limited types 251 12.6 Resource management 257 13 Overall Structure 263 13.1 Library units 263 13.2 Subunits 266 13.3 Child library units 268 13.4 Private child units 272 13.5 Mutually dependent units 279 13.6 Scope, visibility and accessibility 283 13.7 Renaming 287 13.8 Programs, partitions and elaboration 292 Program 3 Rational Reckoner 297 x Contents 14 Object Oriented Programming 301 14.1 Type extension 301 14.2 Polymorphism 307 14.3 Abstract types and interfaces 315 14.4 Primitive operations and tags 318 14.5 Views and redispatching 328 14.6 Private types and extensions 334 14.7 Controlled types 342 14.8 Multiple inheritance 347 14.9 Multiple implementations 353 15 Exceptions 361 15.1 Handling exceptions 361 15.2 Declaring and raising exceptions 364 15.3 Checking and exceptions 370 15.4 Exception occurrences 372 15.5 Exception pragmas and aspects 376 15.6 Scope of exceptions 381 16 Contracts 385 16.1 Aspect specifictions 385 16.2 Preconditions and postconditions 388 16.3 Type invariants 399 16.4 Subtype predicates 405 16.5 Messages 413 17 Numeric Types 417 17.1 Signed integer types 417 17.2 Modular types 423 17.3 Real types 425 17.4 Floating point types 427 17.5 Fixed point types 430 17.6 Decimal types 436 18 Parameterized Types 439 18.1 Discriminated record types 439 18.2 Default discriminants 443 18.3 Variant parts 449 18.4 Discriminants and derived types 453 18.5 Access types and discriminants 456 18.6 Private types and discriminants 463 18.7 Access discriminants 465 19 Generics 469 19.1 Declarations and instantiations 469 19.2 Type parameters 475