The Interpretation of Object-Oriented Programming Languages

295 Pages·2002·9.388 MB·

by  Iain Craig MA, PhD (auth.)

The Interpretation ofObject-Oriented
Programming Languages
Springer-Verlag London Ltd.
lain Craig
The Interpretation
of Object-Oriented
Programming
Languages
Second Edition
, Springer
lain Craig, MA, PhD
British Library Cataloguing in Publication Data
Craig, Iain D.
The interpretation of object-oriented programming
languages. - 2nd ed.
1. Object-oriented programming (Computer science)
2. Programming languages (Electronic computers)
1. Title
005.1'17
ISBN 978-1-85233-547-2
Library of Congress Cataloging-in-Publication Data
Craig, 1.
The interpretation of object-oriented programming languages / Iain D. Craig.. --2nd ed. .
p.cm.
Includes bibliographical references and index.
ISBN 978-1-85233-547-2 ISBN978-1-4471-0199-4 (eBook)
DOI 10.1007/978-1-4471-0199-4
1. Object-oriented programming (Computer science) 1. Title.
QA76.64 .C73 2001
005.l'17-dc21
2001040621
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ISBN 978-1-85233-547-2
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© Springer-Verlag London 2002
Origina1ly published by Springer-Verlag London Limited in 2002
First published 2000
Second edition 2002
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For Adam
Preface to the Second Edition
I was extremely surprised to learn that this book was so wellreceived;I was
even more surprised when a second edition was proposed. I had realised that
there was a need for a book such as this but had not thought that the need
was as great; I really wrote the book for myself, in order better to organise
my thoughts on object-oriented languages and better to understand them.
For the second edition, I have found and corrected mistakes and have
added a completely new chapter on the C# language. The chapteron mixed
paradigm languages has been relegated to an appendix, and a new appendix
on the BeCecil language has been added. -
C# isextremely popular. Given its apparent role as the major competitor
to Java, it was clear that a chapter was necessary in which a comparison
could be made. That chapter concentrates on the language and not on the
runtime and support system. C# contributes some new features to the C++
derivatives. The language has rough edges (as Java does still). It will be
interesting to watch its development and to see whether it becomes accepted
more widely.
The appendix on BeCecil is added so that the coverage of Cecil can be
a little more comprehensive. When writing the first edition, I was unable to
obtain copies of the Cecil definition, which turned out to be a much larger
(and more fascinating) document than I had thought. Given the time allo
cated to me for the production of the second edition, it was impossible to
include more on Cecil-a complete chapter seemed necessary. The existence
of BeCecil, a core language, seemed perfect for my needs. Cecil and BeCecil
are ofinterest because they rationalise much ofobject-oriented programming
languages. I believe that weneed more of this and that Cecil points the way
towards the future.
The mixed-paradigm languages chapter was relegated to an appendix be
cause there appears to be little work in the field.
My major disappointment since writing the first edition isthat databases
and prototype-based languages have still failed to converge. The reason for
this is, probably, that prototype-based languages are still a highly specialist
area and the languages that do exist are still research prototypes. There
is an ample literature in the AI area on the combination of prototype-like
structures with long-term storage upon which to base proposals. Perhaps
VIII Preface to the Second Edition
this is either too obscure or acts to deter research. Perhaps there is work out
there that I have not seen.
Acknowledgements. Iwouldfirst liketo thank BeverleyFord, RebeccaMowat
and all at Springerfor their help in producing this and thefirst edition. They
left mealone to get on with it, and answeredquestionsquickly and accurately.
My brother Adam drew the figures and madea variety ofsuggestions; for the
second edition, his comments on what.10 include and what to exclude were
extremelyhelpful. Margaretdeserves specialthanksforher moralsupportand
encouragement, even though she is far away. I would also like to thank my
good friend Walter Connor for his encouragement and for the great kindness
he has shown towards me. Finally,and this seems unjustly neglected, I would
liketo thank those who have bought the book, for,without them, this edition
would not have come about.I hope the book isstill ofuse and willstimulate
people to think about programming languages and the way in which we
program.
lain Craig
Merrion
Dublin
June 2001
Preface
Object-oriented languages are probably the most important development in
computing for many years. They allow us to describe and to model the phys
ical as well as more abstract worlds.They allow us to provide the computa
tional entities wedescribe with a dynamics that isencapsulated, thus leading
to a more distributed notion of state, a notion which, inter alia, makes pro
gramming and analysis somewhat more tractable.
Unfortunately,ifone wants to understand the concepts that are currently
employed in object-oriented languages, one must refer to the proceedings of
conferences such as OOPSLA or EGOOP. These proceedings might be hard
to obtain or obscure; in any case, without a background in the area, the
reader will almost certainly encounter concepts which willsend them back to
the literature.
The aim of this book is to provide,in one place, an interpretation of the
primary concepts in object-oriented programming languages. In some cases,
for example, multiple inheritance, there is no single interpretation that is
accepted by all; in such cases, the different approaches are explained. An
attempt has been made to be as comprehensive as possible, but certain con
cepts have been omitted for the reason that they are not often encountered or
they have fallen from grace. The concept of the instantiable module appears
to be one example of this.
This having been said, it was, at all times, considered to be important to
cover as many languages as possible in order to give as great a coverage as
possible. Thus, the reader will find references to many languages that have
been derived from LISP (it must be remembered that a considerable amount
of research into object orientation was done in the LISP and AI communi
ties before it became fashionable or appropriate to software engineering in
general).
Oneareain which morework isrequired isin prototype-basedlangauges;I
believe that they are an extremely important development and that they will
assume considerableimportanceas time progresses. However,there have only
been a very fewlarge-scaleattempts at producing prototype-based languages
and the area is still a relatively immature one. The relationships between
prototype-based languages and databases have yet to be explored (and one
might find some interesting advances), as has reflection.
X Preface
My own research area of computational reflection is also included in this
book. I have,though, been extremely careful only to include material that is
directly relevant to the rest of the book and not to be speculative in what
I have included. There is, contrary to the view of some, a great deal more
work required in the area of computational reflection and its implications
for computing in general are insufficiently clear. The chapter on reflection is,
therefore, less wide-ranging and less "aggressive" than I would have liked.
Having read the chapter, the interested reader should try to read the imple
mentation chapters in Goldbergand Robson's excellent bookon Smalltalk-80
(the so-called "Blue Book"). The book is, sadly, out of print, but many li
braries still carry copies; it is an exciting book and, for those interested in
reflection, amply repays the effort required to obtain it.
Finally, I have included a chapter on a so-called 'mixed paradigm'
language, one combining functional and object-oriented concepts. Mixed
paradigm languages combine the best features of different ways of constru
ing programming and computation. It is possible that research into mixed
paradigm languages willpresent us with new concepts and approaches to the
programming process. The combination I have adopted in this book appears
to hold out the promise that program transformation can be performed in
various ways; in particular, it suggests that, if we include reflective capa
bilities in such a language, we can engage in meta-programming in various
ways, one of which is program transformation. Given the general policy on
speculation, these issues are not considered further.
Acknowledgements. I would like to thank Gunter Blaschek for his review of
the manuscript;his comments havehelped considerably.Next,Iwould liketo
thank my brother Adam for drawing the figures, for reading the manuscript
and for suggesting ways in which the text could be made easier to read.
My wife, as ever,has supported me constantly throughout the writing of the
manuscript and has often acted as asounding board when I have been unsure
as to how I should phrase things (and has always urged me to continue when
things looked bad);for this, I thank her.Rebecca (Moore) Mowat ofSpringer
deservesspecial thanksfor her calm attitude to the writingand completion of
the manuscript during a period in which I had to pay considerable attention
to other matters.
lain Craig
Merrion
Dublin
December 1999
Contents
1. Introduction ... .................. .. .... .... .. .... .... .... . 1
1.1 Introduction .. ....... ..... ...... .... .. .. .. ..... .. .. .... 1
1.2 Essential Properties of Objects ........................... 2
1.3 Objects and Messages. .................................. 5
1.4 Pure and Impure Languages. ............................ 7
1.5 Mixed-Paradigm Languages.............................. 8
1.6 Organization of this Book 8
2. Class Fundamentals.. ...... .......... .............. ....... 13
2.1 Introduction. .. ..... ... ..... .... ........ .... ... ........ 13
2.2 Classes.. ......... .. ... ..... .. .. .. .. .. .. .. ..... ........ 15
2.3 Instances. .... .. .. ...... ... .... .. .... .... .... ...... .... 19
2.4 Slots and Methods...................................... 21
2.5 Slot Access ............................................ 22
2.6 Visibility and Accessibility ............................... 24
2.7 Instance Creation 29
2.8 Inheritance.. .... .......... .... ............. .. ......... 32
2.8.1 Introduction. .... .. ....... .... ... ....... ... ..... . 32
2.8.2 Definition of Inheritance 33
2.9 Abstract Classes 38
2.10 Iterators 42
2.11 Part Objects. .......................................... 46
3. Prototype and Actor Languages. .... ..................... 53
3.1 Introduction .. ..... .... .. .. ...... ... .... ... .... ........ 53
3.2 Prototype Languages 53
3.2.1 The Concept of the Prototype 54
3.2.2 Slots and Methods................................ 59
3.2.3 Message Passing 60
3.2.4 Creating New Objects 61
3.2.5 Delegation and Shared Structure " 62
3.3 Methods in Prototype Languages ......................... 66
3.4 Actor Languages. ...................................... 67
3.4.1 Introduction .... .. .. ..... .. .. .. ......... ......... 67