Object-oriented Software in Ada 95

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98 Data structures 7.5.1 Constrained vs. unconstrained discriminants Using the last definition of type Person: Declaration The object Mike is Comment Mike: Person; Unconstrained The variable Mike may be compared with or assigned any other instance of Person. Mike: Person(4); Constrained May only be assigned or compared with another Person(4). 7.5.2 Restrictions on a discriminant A discriminant must be a discrete type or access type. If it is an access type then the record must be limited. This unfortunately means that a Float cannot be used as a discriminant to a record. 7.6 Variant records There will be occasions when a data structure contains data items that are mutually exclusive. For example, in a description of a person who may be a Lecturer or a Student the data members are: Data member Belongs to Description Name Both a Lecturer The name of the person. and a Student Class_Size Lecturer The size of the group that the lecturer teaches. Full_Time Grade Student Whether or not the student is full-time or part-time. The mark out of 100 that the student gains at the end of the course. In this example the storage for Class_Size can overlay all or part of the storage for Full_Time and Grade as the components: • Class_Size • Full_Time and Grade of the data structure will not be used simultaneously. This can be visualized as: role -> Student Name Full_Time grade role -> Lecturer Name Class_Size © M A Smith - May not be reproduced without permission
Data structures 99 In Ada a variant record allows two or more data items to occupy the same physical storage. This will result in a lower memory usage for the data in a program. However, access to the variant components must be carefully controlled to prevent information being stored or extracted as the wrong type. For example, if the record represents a lecturer then it should not be possible to access the component Full_Time as this is only present when the record represents a student. Ada with its strict typing will prevent such occurrences. The data structure to represent either a lecturer or a student is defined as: type Occupation is (Lecturer, Student); type Mark is range 0 .. 100; subtype Str_Range is Natural range 0 .. 20; type Person( Chs : Str_Range :=0; Role: Occupation:=Student ) is record Name : String( 1 .. Chs ); --Name as string case Role is --Variant record when Lecturer => -- Remember storage overlaid Class_Size: Positive; --Size of taught class when Student => Grade : Mark; --Mark for course Full_Time : Boolean := True; --Attendance mode end case; end record; Note: If one discriminant item is given a default value than all discriminant items that follow must also be given a default value. Using the above declaration of Person allows the following assignments to be made: declare Mike : Person; --Unconstrained Clive: Person; --Unconstrained Brian: Person(5,Student); --Constrained begin Mike :=(4, Lecturer, Name=>"Mike", Class_Size=>36); Clive:=(5, Student, Name=>"Clive", Grade=>70,Full_Time=>True); -- insert -- end; In Ada, this process is safe as the compiler will check and disallow access to a variant part which is not specified by the discriminant. For example, if the following statements were inserted at the point -- insert - - above, they would be flagged as invalid at either compile-time or run-time. Invalid statement Clive.Role:= STUDENT Mike.Grade:= 0 Brian := (5, Lecturer, Name=>"Brian", Class_Size=>36); Reason Not allowed to change just a discriminant as this would allow data to be modified/extracted as the wrong type. Detectable at compile-time. Access to a component of the data structure which is not active. Mike is a lecturer and hence has no grade score. Detected at run-time. The object Brian is constrained to be a student. Detectable at compile-time. © M A Smith - May not be reproduced without permission
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Contents CONTENTS .................
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vi Contents 4.21 EXERCISES.........
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viii Contents 10.1 INTRODUCTION ...
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x Contents 16.8.1 Converting a base
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xii Contents 23.6.3 The specificati
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Preface This book is aimed at stude
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xvi Actual parameter Preface The ph
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xviii Elaboration Preface At run-ti
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xx Object Preface An instance of a
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1 Introduction to programming 1 Int
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Introduction to programming 3 they
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Introduction to programming 5 • T
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Introduction to programming 7 The s
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Introduction to programming 9 Line
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Introduction to programming 11 Cost
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Introduction to programming 13 In t
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Introduction to programming 15 For
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Introduction to programming 17 •
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Software design 19 In software the
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Software design 21 2.4 The class In
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Software design 23 Inheritance diag
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25 Ada introduction: Part 1 3 Ada i
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Ada introduction: Part 1 27 3.3.2 C
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Ada introduction: Part 1 29 can be
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Ada introduction: Part 1 31 with Ad
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Ada introduction: Part 1 33 To inpu
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Ada introduction: Part 1 35 Functio
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Ada introduction: Part 1 37 3.14 Ex
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Note: In reality the floating point
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Ada introduction: Part 2 41 4.4 Mod
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Ada introduction: Part 2 43 4.7.2 I
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Ada introduction: Part 2 45 For exa
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Page 71 and 72: Ada introduction: Part 2 49 4.12 Co
Page 73 and 74: Ada introduction: Part 2 51 4.13.1
Page 75 and 76: Ada introduction: Part 2 53 Note 3
Page 77 and 78: Ada introduction: Part 2 55 if Ch i
Page 79 and 80: Ada introduction: Part 2 57 For exa
Page 81 and 82: Ada introduction: Part 2 59 type Mi
Page 83 and 84: Procedures and functions 61 The fun
Page 85 and 86: Procedures and functions 63 The maj
Page 87 and 88: Procedures and functions 65 Mode Al
Page 89 and 90: Procedures and functions 67 The pro
Page 91 and 92: Procedures and functions 69 5.8 Dif
Page 93 and 94: Procedures and functions 71 Note: T
Page 95 and 96: 6 Packages as classes This chapter
Page 97 and 98: Packages as classes 75 6.3.1 An obj
Page 99 and 100: Packages as classes 77 package Clas
Page 101 and 102: Packages as classes 79 The body of
Page 103 and 104: Packages as classes 81 Thus without
Page 105 and 106: Packages as classes 83 6.9 Type pri
Page 107 and 108: Packages as classes 85 which when r
Page 109 and 110: Packages as classes 87 The Ada spec
Page 111 and 112: The main body of the program proces
Page 113 and 114: Packages as classes 91 The procedur
Page 115 and 116: Packages as classes 93 Construct th
Page 117 and 118: Data structures 95 This initializat
Page 119: Data structures 97 Then an assignme
Page 123 and 124: Data structures 101 7.10 Exercises
Page 125 and 126: which when combined with appropriat
Page 127 and 128: Arrays 105 with Ada.Text_Io, Class_
Page 129 and 130: Arrays 107 8.3.1 Putting it all tog
Page 131 and 132: Arrays 109 8.4.1 The class Board Th
Page 133 and 134: Arrays 111 8.4.4 The class Board Th
Page 135 and 136: Arrays 113 8.4.5 Putting it all tog
Page 137 and 138: Arrays 115 8.5.2 Attributes of mult
Page 139 and 140: Arrays 117 The following code would
Page 141 and 142: Arrays 119 This type is defined in
Page 143 and 144: Arrays 121 In the implementation of
Page 145 and 146: Arrays 123 The Ada specification of
Page 147 and 148: Arrays 125 The function valid check
Page 149 and 150: 9 Case study: Design of a game This
Page 151 and 152: Case study: Design of a game 129 A
Page 153 and 154: Case study: Design of a game 131 Co
Page 155 and 156: Case study: Design of a game 133 Cu
Page 157 and 158: Case study: Design of a game 135 --
Page 159 and 160: The specification for the class Cel
Page 161 and 162: Case study: Design of a game 139 pr
Page 163 and 164: Case study: Design of a game 141 Th
Page 165 and 166: Case study: Design of a game 143 Th
Page 167 and 168: Case study: Design of a game 145 In
Page 169 and 170: 10 Inheritance This chapter introdu
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Two instances of the class Interest
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Inheritance 151 The two classes Acc
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Inheritance 153 which when run, wou
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Inheritance 155 The specialization
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Inheritance 157 Note: The methods o
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Inheritance 159 10.7.1 Putting it a
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Inheritance 161 10.8.1 Implementati
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10.9 Hiding the base class methods
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Inheritance 165 • For an object o
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Exceptions 167 11.1.1 Putting it al
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Exceptions 169 11.3 Private child A
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12 Defining new operators This chap
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Exceptions 173 Using the above pack
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Exceptions 175 The function Rat_Con
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Exceptions 177 12.3.1 Overloading =
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Exceptions 179 The overloaded defin
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Exceptions 181 12.3.5 use type A mo
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13 Exceptions This chapter looks at
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Exceptions 185 Note: The object Eve
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Exceptions 187 A program to demonst
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Exceptions 189 package body Class_S
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14 Generics This chapter looks at g
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Exceptions 193 The above generic pr
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Exceptions 195 14.3 Generic stack T
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Exceptions 197 14.3.1 Putting it al
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Thus, an instantiation of a procedu
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Exceptions 201 14.5 Sorting Some of
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14.6.1 Putting it all together Exce
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Exceptions 205 An efficient impleme
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Exceptions 207 The implementation o
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15 Dynamic memory allocation This c
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Dynamic memory allocation 211 In a
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Dynamic memory allocation 213 One w
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Dynamic memory allocation 215 15.2.
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Dynamic memory allocation 217 The p
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Dynamic memory allocation 221 A ben
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15.7 Attributes 'Access and 'Unchec
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16 Polymorphism In the processes de
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Polymorphism 229 This can be implem
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Polymorphism 231 16.2.1 Putting it
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Polymorphism 233 Figure 16.3 Hetero
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Polymorphism 235 16.5 A building in
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Polymorphism 237 An example interac
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Polymorphism 239 The conversion fro
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Polymorphism 241 Screen Observed Ob
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Polymorphism 243 The method Add_Obs
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Polymorphism 245 The functions vali
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Polymorphism 247 The driver program
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17 Containers This chapter describe
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Containers 251 This mirrors closely
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Containers 253 will produce the fol
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Containers 255 When an instance of
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Containers 257 When the iterator Co
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Containers 259 In the implementatio
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Containers 261 A deep copy of this
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Containers 263 • If the objects o
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Containers 265 17.6.1 Ada specifica
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Containers 267 The procedure Adjust
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17.7 A set Containers 269 Using as
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Containers 271 17.7.1 Putting it al
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18 Input and output This chapter de
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Input and output 275 18.2 Reading a
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Input and output 277 Then the follo
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Input and output 279 18.5 Self-asse
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Persistence 281 A program to implem
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Persistence 283 with Ada.Strings.Un
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Persistence 285 The process to add
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Persistence 287 The procedure Add u
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20 Tasks This chapter describes the
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Tasks 291 The execution of the abov
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Tasks 293 Likewise, the task Task_I
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Tasks 295 20.4 Protected type In es
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Tasks 297 The implementation of the
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Tasks 299 to the entry prevents the
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Note: 20.7.1 Accept alternative Tas
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Tasks 303 the implementation of whi
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Tasks 305 • How can a task select
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System programming 307 21.1.1 Putti
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System programming 309 The followin
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22 A text user interface This chapt
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A Text user interface 313 Note: The
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A Text user interface 315 with Clas
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A Text user interface 317 Window_St
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A Text user interface 319 The follo
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A Text user interface 321 package C
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A Text user interface 323 with Clas
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A Text user interface 325 function
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A Text user interface 327 • What
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TUI the implementation 329 23.1.1 S
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TUI the implementation 331 package
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TUI the implementation 333 23.2.4 T
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TUI the implementation 335 with Ada
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TUI the implementation 337 The Inpu
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TUI the implementation 339 procedur
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TUI the implementation 341 New_Line
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TUI the implementation 343 private
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TUI the implementation 345 The proc
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TUI the implementation 349 with Pac
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TUI the implementation 351 Method S
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TUI the implementation 355 The proc
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24 Scope of declared objects This c
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Proc_2_2 Proc_1_1 Proc_2_1 Proc_2_2
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25 Mixed language programming This
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Mixed language programming 363 3 Tr
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Mixed language programming 365 /* *
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Appendix A 367 if Temp < 15 then Pu
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Appendix A 369 package body Class_I
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Appendix B: Components of Ada B.1 R
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T'Digits The decimal precision. Uni
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Appendix B 375 access enumeration E
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Appendix B 377 B.8.2Ada information
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Appendix C 379 package Standard is
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Appendix C 381 type Character is (n
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Appendix C 383 package Ada.IO_Excep
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Appendix C 385 --Specification of l
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Appendix C 387 procedure Get(File :
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Appendix C 389 procedure Get(Item :
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Appendix C 391 package Ada.Characte
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Appendix C 393 --Conversion, Concat
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Appendix C 395 return Natural; Goin
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Appendix C 397 Right : in Bounded_S
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Appendix C 399 Count : out size_t;
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Appendix C 401 C.14 The Package Ada
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Appendix C 403 --Storage-related De
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Appendix D 405 with Ada.Text_Io; us
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Appendix D 407 with Ada.Text_Io, Ad
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Appendix D 409 package Class_Perfor
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Appendix D 411 declare Kb : constan
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Appendix D 413 package body Class_B
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Appendix D 415 The instantiation of
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Appendix D 417 with Ada.Text_Io, Ad
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References Intermetrics (1995) Ada
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Index 421 'class, 233 Class attribu
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Index 423 + dyadic, 53 monadic, 54
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Object-oriented Software in Ada 95

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