VIRTUAL CLASSES and their Implementation. Ole Lehrmann Madsen Aarhus University Alexandra Institute A/S Mj lner Informatics A/S

Transcription

1 VIRTUAL CLASSES ad their Implemetatio Ole Lehrma Madse Aarhs Uiversity Alexadra Istitte A/S Mj ler Iformatics A/S

2 Cotets 1. Itrodctio & backgrod 2. Uificatio of abstractio mechaisms 3. Virtal patters 4. Typig isses 5. Implemetatio isses 6. Smmary ETAPS 2001 ' Ole Lehrma Madse 2

3 Origis of BETA Based o the Scadiavia approach to object-orietatio Sccessor to Simla The Mj ler System Developmet eviromet for BETA Beta was origially developed by: Bet Br Kristese Ole Lehrma Madse Birger M ller-pederse Kriste Nygaard Importat cotribtors to BETA ad the Mj ler System J rge Lidskov Kdse, Elmer Sadvad, Peter Aderse ad may more ETAPS 2001 ' Ole Lehrma Madse 3

4 Desig goals for BETA Oe lagage for desig ad implemetatio Good modelig lagage Efficiet programmig lagage Simple ad geeral Scheme, Smalltalk, Self Statically typed As mch as possible Good spport for strctrig ad abstractio Uified paradigm Neither pre OO or mlti-paradigm ETAPS 2001 ' Ole Lehrma Madse 4

5 Abstractio i BETA Coceptal framework The coceptal meas for orgaizig ad derstadig pheomea ad cocepts Idepedet of formal lagages Shold be richer tha the formal lagages BETA patter Uificatio of class, procedre, type, exceptio,... Towards the ltimate abstractio mechaism Cocepts represeted as patters Pheomea represeted as objects ETAPS 2001 ' Ole Lehrma Madse 5

6 Beefits of object-orietatio Uifyig perspective o major elemets of software developmet aalysis, desig, implemetatio data bases, object distribtio Good spport for modelig programs reflect reality i a atral way Good spport for extesibility & rese class, sbclass, virtal,... frameworks, biary compoets, desig-, architectral patters,... ETAPS 2001 ' Ole Lehrma Madse 6

7 2. Uificatio of abstractio mechaisms Abstractio mechaism: Class : A patter for creatig istaces A patter for creatig objects Procedre: A patter for creatig evet-seqeces Fctio, iterface, process type, geeric class, exceptio type, Patters for creatig varios kids of istaces ETAPS 2001 ' Ole Lehrma Madse 7

8 The patter I BETA, class, procedre, ad other abstractio mechaisms have bee ified ito The Patter Uiform treatmet of all abstractio mechaisms: F Procedre, class,... Class-iheritace, procedre-iheritace,... Virtal procedre, virtal class, Nested procedre, ested class, Procedre variable, class variable,... ETAPS 2001 ' Ole Lehrma Madse 8

9 Procedre activatios & objects class Set: {... proc isert(e: ref object): { ix: obj iteger do ; e R[ix]; ; }; R: array of object }; proc mai(): { Joe: ref Perso; S: ref Set; do ew Perso Joe; ew Set S; S.isert(Joe); } Mai DYN: Joe: S: Isert DYN: OBJ: e: ix: 0 Perso... Set R: ETAPS 2001 ' Ole Lehrma Madse 9

10 Nested classes & procedres class Set: {... class Elemet: { elm: ref object; ext: ref Elemet; } proc isert(e: ref object): { proc ewelm(e: ): { } do }; }; Isert DYN: OBJ:... ewelm DYN: STAT:... Set... Elemet STAT:... OBJ: STAT: object-referece for procedre activatio eclosig object for object or activatio ETAPS 2001 ' Ole Lehrma Madse 10

11 Objects ad procedre activatios Object: Data-items:... Static lik: eclosig object/procedre Procedre-activatio: Data-items: Parameters Local variables Static lik: eclosig object/procedre Dyamic lik: caller ETAPS 2001 ' Ole Lehrma Madse 11

12 Procedre call M: ref R.isert ew R.isert(Joe) M; M.execte Mai DYN: Joe: S: M: Isert DYN: OBJ: e: ix: 0 Set... Perso... ETAPS 2001 ' Ole Lehrma Madse 12

13 Patter: class & procedre Perso: { }; Set: { isert(e: ref object): { do }; }; mai(): { Joe: ref Perso; S: ref Set; do ew Perso Joe ; ew Set S ; S.isert(Joe); } Static lik: if estig Dyamic lik: if do-part Parameters Data-items Object layot STAT: DYN: parameters data-items ETAPS 2001 ' Ole Lehrma Madse 13

14 Uiform abstractio mechaisms patter class fctio iterface procedre exceptio process The Patter The ltimate abstractio mechaism A geeralizatio/ificatio of class, procedre,fctio, exceptio, iterface, process, geeric class,... ETAPS 2001 ' Ole Lehrma Madse 14

15 Beefits of the ificatio class procedre exceptio process... Patter Sbpatter Virtal patter Patter variable Nested patter ETAPS 2001 ' Ole Lehrma Madse 15

16 Examples of ew possibilities Sbpatter : classificatio of actios - iheritace for procedres sig ier Virtal patter: OO geericity Patter variable: procedres & classes as first class vales; higher order procedres & classes Nested patter: ehaced modelig capability; object with several iterfaces ETAPS 2001 ' Ole Lehrma Madse 16

17 Sbclass: classificatio of objects Record: { Key: ref Idetificatio }; Book: Record { Athor: ref Perso; Title: ref Text }; Perso: Record { Name: ref Text; Sex: ref SexType }; Employee: Perso { Salary: obj Iteger; Positio: ref PositioType }; Stdet: Perso { Stats: ref StatsType }; Book Record Perso Employee Stdet ETAPS 2001 ' Ole Lehrma Madse 17

18 Actio seqece geeralizatio L: obj Set; M: obj Semaphore; Pt(e: obj iteger): { do M.wait; L.pt(e); M.sigal }; iteger Get(): { do M.wait; L.get() e; M.sigal retr e } Pt: M.wait L.pt(e) M.sigal Get: M.wait L.get() e M.sigal Geeralized evet seqece: M.wait * M.sigal ETAPS 2001 ' Ole Lehrma Madse 18

19 Procedre specializatio Bffer: moitor { L: obj Set; pt(e: obj iteger): etry { do L.pt(e) };... }; B: obj Bffer B.pt(123) Moitor: { M: obj semaphore; etry: { do M.wait; INNER; M.sigal };... }; M.wait INNER M.sigal L.pt(e) ETAPS 2001 ' Ole Lehrma Madse 19

20 Iheritace characterizatio P. Weger, S. Zdoik: Relatio betwee a sbclass ad its sperclass Name compatible Sigatre compatible Strctrally compatible BETA Behaviorally compatible ETAPS 2001 ' Ole Lehrma Madse 20

21 3. Virtal patter Virtal procedre Virtal class Virtal class: A lagage costrct for defiig geeric classes Alterative to: Parameterized class F F Template class i C++ Geeric class i Eiffel ETAPS 2001 ' Ole Lehrma Madse 21

22 Set of objects class Set: { proc isert(e: ref object): { do top+1 top; E R[top] :< describes that }; display is a proc display:< {}; virtal procedre R: array[100] ref object; } top: obj iteger ETAPS 2001 ' Ole Lehrma Madse 22

23 Virtal procedre bidig ::< class StdetSet: Set virtal procedre { display()::< bidig of display { crret: ref Object do (for i: top repeat R[i] crret; (Stdet)crret.prit() for) }; Cast to Stdet } ETAPS 2001 ' Ole Lehrma Madse 23

24 Geeric class Set :< describes that elemet is a virtal class class Set: { class elemet:< object; proc isert(e: ref elemet): {...}; proc display():< {}; } R: array[100] ref elemet; top: obj iteger ETAPS 2001 ' Ole Lehrma Madse 24

25 StdetSet: sbclass of Set class StdetSet: Set { elemet::< Stdet; display()::< { crret: ref elemet do (for i: top repeat R[i] crret; crret.prit() for) }; } ::< bidig of elemet to Stdet ::< virtal procedre bidig of display crret is of type elemet No cast: crret: Stdet has a prit operatio ETAPS 2001 ' Ole Lehrma Madse 25

26 Frther specializatio class CSstdetSet: StdetSet { elemet::< CSstdet; } object Stdet Set CSstdet StdetSet CSstdetSet ETAPS 2001 ' Ole Lehrma Madse 26

27 Local virtal class patter Graph: { Node:< { coected: obj boolea }; Lik:< { sorce,dest: ref Node }; Coect(S,D: ref Node ):< {L: ref Lik do ew Lik L; S L.sorce; D L.dest; tre S.coected D.coected; ier } } ETAPS 2001 ' Ole Lehrma Madse 27

28 Local virtal class patter bidigs DisplayableGraph: Graph { Node::< { dispsymb: ref DisplaySymbol }; Lik::< { displie: ref DisplayLie }; Coect(DL: ref DisplayLie)::< { do DL L.dispLie; INNER }; Display:< {... } } ETAPS 2001 ' Ole Lehrma Madse 28

29 Extedig virtal class patters DistaceGraph: Graph { Node::< { ame: ref text }; Lik::< { distace: obj iteger }; Coect(dist: obj iteger)::< { do dist L.distace; INNER }; } Graph::Node DistaceGraph::Node DisplayableGraph::Node ETAPS 2001 ' Ole Lehrma Madse 29

30 Virtal class verss parameterized class Ca both express the same basic elemets Virtal class: A simple extesio to OO lagages Aalogos to virtal procedre Class = type A geeric class is a real class StdetSet is a sbclass of Set Covariace + fial bidigs Mtally recrsive classes ETAPS 2001 ' Ole Lehrma Madse 30

31 Smmary of virtal patters A: { V:< Q; W:< P{... }; }; AA: A { V::< QQ; W::< {... } }; AAA: AA { V:: QQQ W:: {... }; } Virtal declaratios Frther bidigs Fial bidigs ETAPS 2001 ' Ole Lehrma Madse 31

32 Virtal procedre & class patters A: { V:< Q; W:< P{... }; do V(e1,e2,e3) x; W(e1,e2,e3) x; }; A: { V:< Q; W:< P{... }; S: ref V; R: ref W do ew V S; ew W R }; Virtal procedre patter: Istaces are created ad exected Virtal class patter: Istaces are created ad assiged to variables ETAPS 2001 ' Ole Lehrma Madse 32

33 4. Typig isses Covariace Reverse assigmet Static typig ETAPS 2001 ' Ole Lehrma Madse 33

34 Covariace Poit: { ThisClass:< Poit; x,y: obj iteger; Emlatio of thisclass sig virtal patter } eqal(p: ref ThisClass):< { eq: obj boolea do (x = p.x) ad (y = p.y) eq; } ier; retr eq ETAPS 2001 ' Ole Lehrma Madse 34

35 ColorPoit ColorPoit: Poit { ThisClass::< ColorPoit; c: obj Color; Frther bidig of thisclass } eqal::< { do (eq ad (c = p.c)) eq; ier } ETAPS 2001 ' Ole Lehrma Madse 35

36 Type cases Usig sbtype sbstittable variables (dyamic refereces) p1,p2: ref Poit; c1,c2: ref ColorPoit; ew Poit p1; ew ColorPoit c1; ew Poit p2; ew ColorPoit c2 1. p2.eqal(p1) OK r time 2. c2.eqal(c1) OK r time 3. p1.eqal(c1) OK r time 4. c1.eqal(p1) NON OK r time ETAPS 2001 ' Ole Lehrma Madse 36

37 Reverse assigmet p1: ref Poit; c1: ref ColorPoit; e: ref c1.eqal c1 p1 OK - compile time p1 c1 OK? - r time - reverse assigmet c1.eqal(p1) ew c1.eqal e; p1 e.p; e(); Poit: { ThisClass:< Poit; } eqal(p: ref ThisClass):< { do... };... retr eq ETAPS 2001 ' Ole Lehrma Madse 37

38 Desirable properties At most 2 possible: 1. Sbtype sbstittability 2. Covariace 3. Static type checkig 4. Class = type sbclass = sbtype 5. Mtable state 6. Message sed 7. Modlar type checkig ETAPS 2001 ' Ole Lehrma Madse 38

39 Cases for static typig Type gards Exact types Fial bidigs No ivocatio of virtal procedre with virtal argmets Nested virtal class patters class families ETAPS 2001 ' Ole Lehrma Madse 39

40 Frther work o virtal classes Erik Erst Kreste Krab Thorp Mads Torgerse A. Igarashi Bejami Pierce David Shag Kim Brce Marti Odersky Philip Wadler Ad others Virtal types i Java Uifyig geericity GBETA... a geeralizatio of BETA Alteratives to virtal classes Mathematical fodatio Block strctre ECOOP OOPSLA FOOL ETAPS 2001 ' Ole Lehrma Madse 40

41 5. Implemetatio isses R-time orgaizatio Allocatio of objects Virtal patters Sematic aalysis ETAPS 2001 ' Ole Lehrma Madse 41

42 Allocatio of objects Procedre activatios are first-class objects A referece ca be obtaied to a procedreactivatio Reqires heap-allocatio - i geeral Room for optimizatio Stack allocatio of procedre activatios ETAPS 2001 ' Ole Lehrma Madse 42

43 Virtal class implemetatio A virtal patter is istatiated throgh a virtal dispatch table Object X: Virtal Dispatch Table Code/templates f1:... f2:... f3:... ETAPS 2001 ' Ole Lehrma Madse 43

44 The problem: virtal procedre bidig Declaratio: proc V():<... Bidig 1: V ()::<... Bidig 2: V ()::<... Virtal procedre applicatio: V(); Dyamic bidig: the actal istace of V geerated at r-time Static bidig: the bidig of V kow o compile-time; The static bidig is eeded for type checkig of parameters ETAPS 2001 ' Ole Lehrma Madse 44

45 The problem: virtal class bidig Declaratio: class V:<... Bidig 1: V ::<... Bidig 2: V ::<... Variable declaratio: X: ref V Use of istace of virtal class: X.f() Dyamic bidig: the actal istace of V geerated at r-time Static bidig: the bidig of V kow at compile-time; For X this is the type of X Static bidig is eeded for type checkig ETAPS 2001 ' Ole Lehrma Madse 45

46 Partial problems i sematic aalysis Easy: Nested procedres o virtals Nested classes o virtals Virtal procedre bidig o estig Easy: Virtal class bidig o estig Virtal procedre bidig with estig Hard: Virtal class bidig with estig ETAPS 2001 ' Ole Lehrma Madse 46

47 Simple virtal class bidig StdetSet: PersoSet: SetWithMark: Set: elm::< Stdet elm::< Perso last: ref elm elm:< object Dyamic bidig Static bidig object Mai: S: ref PersoSet; ew StdetSet S S.last.prit() Type of last? Perso: prit(): Stdet ETAPS 2001 ' Ole Lehrma Madse 47

48 Geeral example PersoSet: elm::< Perso SetWithPort: Set: elm:< object PortWithViewer: Port: last: ref elm Viewer: ShowLast: ;last.prit(); ETAPS 2001 ' Ole Lehrma Madse 48

49 6. Smmary Simple ad geeral lagage Based o a rich coceptal framework For modelig ad implemetatio The patter is a powerfl abstractio mechaism Virtal patters A simple geeralizatio of virtal procedres Powerfl meas for defiig geeric classes Geeral estig of patters Patters as first class vales Classless objects Cocrrecy Uified paradigm ETAPS 2001 ' Ole Lehrma Madse 49

50 The Mj ler System A idstrial stadard matre eviromet for developmet of BETA programs For a example of a large applicatio developed i BETA, see the demo of CPN/Tools: A Tool for Editig ad Simlatig Colored Petri Nets M. Beadoi-Lafo, W. Mackay, M. Jese, P. Aderse, P. Jaecek, M. Lasse, K. Ld, K. Mortese, S. Mck, A. Ratzer, K. Rav, S. Christese, K. Jese (Aarhs Uiversity) Thrsday 5/ ETAPS 2001 ' Ole Lehrma Madse 50

51 Cotact address Ole Lehrma Madse Compter Sciece Departmet Aarhs Uiversity Aabogade 34, DK-8200 Aarhs N DENMARK olmadse@daimi.a.dk Get a free Mj ler System sales@mjoler.com ETAPS 2001 ' Ole Lehrma Madse 51