Eif f el: Analysis, Design and Programming Bertrand Meyer (Nadia - PowerPoint PPT Presentation

A de A defe ferred fe rred feature ature I n e.g. LI ST : f or t h require not af t er def erred ensure index = old index + 1 end 32

Mixing Mixing deferre deferred and effectiv d and effective featur e features es I n t he same class Ef f ect ive! search ( x : G ) -- Move t o f ir st posit ion af t er current -- where x appears, or af t er if none. do f rom until af t er or else it em = x loop f or t h end end Def er r ed! “Programs with holes” 33

“Do “Don’ n’t call t call us, we’l us, we’ll l call you! call you!” A powerf ul f orm of reuse: � The reusable element def ines a general scheme � Specif ic cases f ill in t he holes in t hat scheme Combine r euse wit h adapt at ion 34

Defe Deferr rred clas d classe ses in Eiff s in Eiffel elBa Base se * CONTAI NER * * * BOX COLLECTI ON TRAVERSABLE * * * * * * I NFI NI TE BAG SET HI ERARCHI CAL LI NEAR FI NI TE * * * * * * * I NTEGER_ BOUNDED UNBOUNDED COUNTABLE TABLE ACTI VE BI LI NEAR I NTERVAL … … * * * * * RESI ZABLE CURSOR_ I NDEXABLE DI SPENSER SEQUENCE STRUCTURE * * ARRAY STRI NG HASH_TABLE STACK QUEUE * def erred 35

Deferr Defe rred cla d classes es for an for anal alys ysis is def erred class VAT inherit TANK f eature in_valve , out _valve : VALVE f ill is -- Fill t he vat . require in_valve.open out _valve.closed def erred ensure in_valve.closed out _valve.closed is_f ull end empt y , is_f ull , is_empt y , gauge , maximum , ... [Ot her f eat ures] ... invariant is_f ull = ( gauge > = 0.97 * maximum ) and ( gauge < = 1.03 * maximum ) end 36

Polymor Polymorph phic data structures ic data structures f l class LI ST [ G ] f eature ... last : G is ... ext end ( x : G ) is ... (SQUARE) end f l : LI ST [ FI GURE ] r : RECTANGLE (TRI ANGLE) s : SQUARE (RECTANGLE) (POLYGON) t : TRI ANGLE p : POLYGON ... f l . ext end ( p ); f l . ext end ( t ); f l . ext end ( s ); f l . ext end ( r ) f rom f l.st ar t until f l.af t er loop f l . it em . display; f l.f ort h end 37

Figure hierar Figure hierarchy (remin chy (reminder) der) display* cent er * * FI GURE r ot at e* move* * * per imet er* OPEN_FI GURE CLOSED_FI GURE display + r ot at e + per imet er + per imet er + move + SEGMENT POLYLI NE + + ELLI P SE POLYGON . . . per imet er ++ side1 . . . RECTANGLE TRI ANGLE per imet er ++ side2 CI RCLE diagonal display ++ r ot at e ++ * def erred display + per imet er ++ move ++ r ot at e + + ef f ect ive SQUARE move + ++ redef ine d 38

Enforcing a Enforcing a type: th type: the pro e problem blem f l . st or e ("FI LE_NAME") ... -- Two year s lat er: f l := ret rieved ("FI LE_NAME“) x := f l . last -- [1] print ( x . diagonal ) -- [2] What ’s wr ong wit h t his? � I f x is declared of t ype RECTANGLE , [1] is invalid. � I f x is declared of t ype FI GURE , [2] is invalid. 39

Enforcing g a a type: : the e Object t Test Opt ional (if omit t ed Expr ession t o be Obj ect -Test Local j ust t est s f or void) t est ed if attached { RECTANGLE } f l . last as r then print ( r . diagonal ) … Do anyt hing else wit h r , guarant eed t o be non-void … and of dynamic t ype (descendant of ) RECTANGLE else print ("Too bad.") end SCOPE of t he Obj ect -Test Local 40

Earlier mechan Earlier mechanism ism: assignmen : assignment attempt t attempt f : FI GURE r : RECTANGLE ... f l . r et r ieve ("FI LE_NAME") f := f l . last r ?= f if r / = Void t hen print ( r . diagonal ) else print ("Too bad.") end 41

As Assi signment a gnment att ttempt empt x ?= y wit h x : A Semant ics: � I f y is at t ached t o an obj ect whose t ype conf or ms t o A , perf or m normal r ef erence assignment . � Ot herwise, make x void. 42

What we h What we have seen ave seen � Basics � Redef init ion � Polymor phism and dynamic binding � I nherit ance and cont ract s � Def erred classes � Polymorphic cont ainers 43

Top Topic ics for t s for today oday � I nher it ance and genericit y: const rained gener icit y � Mult iple inherit ance � Non-conf or ming inher it ance � Covar iance and anchor ed t ypes 44

Inherit Inheritanc ance + Ge + Generi nericity city Unconst rained genericit y LI ST [G] e.g. LI ST [ I NTEGER ], LI ST [ PERSON ] Const r ained gener icit y HASH_TABLE [G, H � > HASHABLE ] VECTOR [ G � > NUMERI C ] 45

Constraine Constrained genericity d genericity class VECTOR [ G ] f eature plus alias "+" ( ot her : VECTOR [ G ]): VECTOR [ G ] -- Sum of cur rent vect or and ot her . require lower = ot her . lower upper = ot her . upper local a , b , c : G do ... See next ... end ... Ot her f eat ur es ... end 46

Adding two vectors Adding two vectors u + v = w 2 = = i i c c a a b b + + 1 47

Constraine Constrained genericity d genericity Body of plus alias "+": create Result . make ( lower , upper ) f rom i := lower until i > upper loop a := it em ( i ) b := ot her . it em ( i ) c := a + b -- Requires “+” operat ion on G! Result . put ( c , i ) i := i + 1 end 48

The s The solut olutio ion Declare class VECTOR as class VECTOR [ G –> NUMERI C ] f eature ... The rest as bef ore ... end Class NUMERI C (f rom t he Kernel Library) provides f eat ures plus alias "+", minus alias "-" and so on. 49

Im Impro proving the solution ving the solution Make VECTOR it self a descendant of NUMERI C , ef f ect ing t he corr esponding f eat ures: class VECTOR [ G –> NUMERI C ] inherit NUMERI C f eature ... Rest as bef ore, including inf ix "+"... end Then it is possible t o def ine v : VECTOR [ I NTEGER ] vv : VECTOR [ VECTOR [ I NTEGER ]] vvv : VECTOR [ VECTOR [ VECTOR [ I NTEGER ]]] 50

In the end In the end.. ... Genericit y is always const rained because LI ST [ G ] is j ust an abbr eviat ion of LI ST [ G -> ANY ] 51

Combining abstracti Combining abstractions ons Given t he classes � TRAI N_CAR, RESTAURANT how would you implement a DI NER? 52

Examples of m Examples of multipl ultiple inheritan e inheritance ce Combining separat e abst ract ions: � Rest aurant , t r ain car � Calculat or , wat ch � Plane, asset � Home, vehicle � Tram, bus 53

Composite fig Com posite figures ures 54

Multiple in Multiple inherit heritance ance: Co : Compos mposite figures ite figures Simple figures A composite figure 55

De Definin fining the n g the notion of otion of co compos mposite figure ite figure cent er LI ST display FI GURE count [ FI GURE ] hide put r ot at e r emove move … … COMPOSI TE_ FI GURE 56

In the In the ove overall structure rall structure LI ST FI GURE [ FI GURE ] OPEN_ CLOSED_ FI GURE FI GURE per imet er * COMPOSI TE_ SEGMENT POLYLI NE P OLYGON FI GURE ELLI PSE per imet er + per imet er + diagonal RECTANGLE CI RCLE per imet er ++ per imet er ++ TRI ANGLE SQUARE per imet er ++ 57

A comp A composit ite e figu figure re as a list as a list bef or e af t er it em f or t h Cur sor 58

Com Composite fig posite figures ures class COMPOSI TE_FI GURE inherit FI GURE LI ST [ FI GURE ] f eature display -- Display each const it uent f igure in t urn. do f rom st ar t until af t er loop it em . display f or t h Requir es dynamic end binding end ... Similarly f or move , rot at e et c. ... end 59

Goin Going g one lev one level el of abstr of abstrac acti tion hig n highe her A simpler f orm of procedures display , move et c. can be obt ained t hr ough t he use of it er at ors Use agent s f or t hat pur pose 60

Multiple inheritance Multipl e inheritance: Combining : Combining abstraction abstractions +, –, < , < =, � , / NUMERI C COMPARABLE > , > =, … … (commut at ive (t ot al or der r ing) r elat ion) I NTEGER REAL COMPLEX STRI NG 61

The Jav The Java- a-C# solu # soluti tion No mult iple inher it ance f or classes “I nt er f aces”: specif icat ion only (but no cont r act s) � Similar t o complet ely def erred classes (wit h no ef f ect ive f eat ure) A class may inherit f rom: � At most one class � Any number of int erf aces 62

Multiple inheritance Multipl e inheritance: Combining : Combining abstraction abstractions +, –, < , < =, � , / NUMERI C COMPARABLE > , > =, … … (commut at ive (t ot al or der r ing) r elat ion) I NTEGER REAL COMPLEX STRI NG 63

How How do we writ do we write e CO COMPARABLE MPARABLE ? def erred class COMPARABLE [ G ] f eature less alias "< " ( x : COMPARABLE [ G ]): BOOLEAN def erred end less_equal alias "< =" ( x : COMPARABLE [ G ]): BOOLEAN do Result := Current < x or Current ~ x end great er alias "> " ( x : COMPARABLE [ G ]): BOOLEAN do Result := x < Current end great er _equal alias "> =" ( x : COMPARABLE [ G ]): BOOLEAN do Result := x < = Current end end 64

Less Lesson ons fr s from t om this exa his exampl ple Typical example of progr am wit h holes We need t he f ull spect rum f r om f ully abst r act (f ully def err ed) t o f ully implement ed classes Mult iple inher it ance is t here t o help us combine abst r act ions 65

Mu Multip ltiple i le inheri heritance: N tance: Name c me clashes shes f B f A ? C 66

Re Resolving nam solving name cl e clashes ashes f B f A rename f as A_f A_f , f C 67

Conseque Consequences nces of of renaming renaming a1 : A f f A B b1 : B c1 : C ... c1 . f rename f as A_f c1 . A_f C A_f , f a1 . f b1 . f I nvalid: � a1 . A_f � b1 . A_f 68

Are Are all name all name clas clashe hes bad s bad? A name clash must be r emoved unless it is: � Under repeat ed inherit ance (i.e. not a real clash) � Bet ween f eat ures of which at most one is ef f ect ive (i.e. ot hers are def er red) 69

Featur Feature me e mergin rging f + A f * B C f * D � Def erred + Ef f ect ive 70

Featur Feature me e mergin rging: with dif g: with differe ferent names nt names class D h + g * f * A B C inherit A rename g as f end B g f h C f rename D h as f � Def erred end + Ef f ect ive f eature ... Renaming end 71

Featur Feature merging: e merging: effective feature effective features f + f + f + A B C f -- f -- D � Def erred + Ef f ect ive -- Undef ine 72

Un Undefin definition ition def erred class T inherit S undef ine v end f eature ... end 73

Mer Merging ging thro through ugh un undefinit definition ion f + f + f + A B C class D f -- inherit A f -- undef ine f end D B � Def erred C undef ine f end + Ef f ect ive f eature -- Undef ine ... end 74

Merging effective feature Merging effective features with di s with different fferent na names mes f + h + g + C B A class D inherit g A f undef ine f end f -- B rename f -- g as f h f undef ine f end D C rename h as f end f eature ... end 75

Accepta Acceptable ble na name clashes me clashes I f inherit ed f eat ures have all t he same names, t here is no harmf ul name clash if : � They all have compat ible signat ur es � At most one of t hem is ef f ect ive Semant ics of such a case: � Merge all f eat ures int o one � I f t here is an ef f ect ive f eat ure, it imposes it s implement at ion 76

Featur Feature merging: e merging: effective feature effective features g + A f + B h + C g f h f D f - f - a1 : A b1 : B c1 : C d1 : D a1 . g b1 . f c1 . h d1 . f 77

A A spe special case of cial case of mu multiple ltiple in inherita heritance nce UNI VERSI TY id _MEMBER TEACHER STUDENT ?? ?? ASSI STANT ???? This is a case of repeat ed inher it ance 78

Indirec Indirect and di t and direct repeat rect repeated inherit ed inheritanc ance A A C B D D 79

Multiple is Multiple is al also rep so repeate eated inheritanc d inheritance copy A t ypical case: ANY is_equal copy ++ C LI ST is_equal ++ copy C_copy D is_equal C_is_equal ?? 80

Sha Sharing ring an and re d replicatio plication f A g g g_c g g_b C B D Feat ures such as f , not renamed along any of t he inherit ance pat hs, will be shared. Feat ures such as g , inher it ed under dif f erent names, will be replicat ed. 81

The nee The need d for s for selec elect A pot ent ial ambiguit y ar ises because of polymor phism and dynamic binding: copy ANY is_equal a1 : ANY d1 : D C LI ST … copy ++ is_equal ++ a1 := d1 copy C_copy a . copy ( … ) is_equal C_is_equal D 82

Removing th Removing the a e ambiguity mbiguity class D inherit LI ST [ T ] select copy , is_equal end C rename copy as C_copy , is_equal as C_is_equal , ... end 83

Whe When n is a name is a name clas clash h acce accept ptabl ble? (Bet ween n f eat ures of a class, all wit h t he same name, immediat e or inherit ed.) � They must all have compat ible signat ures. � I f more t han one is ef f ect ive, t hey must all come f rom a common ancest or f eat ure under repeat ed inher it ance. 84

Another Another app applicatio lication of r n of renaming enaming Provide locally bet t er adapt ed t erminology. Example: child ( TREE ); subwindow ( WI NDOW ) 85

Multiple In Multiple Inherit heritan ance and C ce and Class T lass Tables ables Why does t his not work wit h mult iple subt yping ? Can we st ill do O(1) lookup ? 86

The dy The dynam namic ic bind bindin ing fun g funct ctio ion Name × St at icType × DynamicType � Code 87

The dy The dynam namic ic bind bindin ing fun g funct ctio ion (Name × St at icType) � DynamicType � Code 88

The dy The dynam namic ic bind bindin ing fun g funct ctio ion (Name × St at icType) � DynamicType � Code St at ic Dynamic 89

Feature Tables Featu re Tables Dynamic Type A B C St at ic Type f of A Code Point er Code Point er Code Point er g of A Code Point er Code Point er Code Point er h of B Code Point er g of C Code Point er 90

Non-confor Non-conformi ming inheritanc ng inheritance class ARRAY [ G ] f eature ... lower , upper : I NTEGER r esize ( l , u : I NTEGER ) ensure lower = l ; upper = u LI ST end ARRAY class ARRAYED_LI ST [ G ] inherit LI ST [ G ] ARRAY [ G ] ARRAYED_LI ST ... invariant st ar t s_f r om_1 : lower = 1 end a : ARRAY [ I NTEGER ]; l : ARRAYED_LI ST [ I NTEGER ] ... Class invar iant a := l violat ion a.r esize (-10, 10) 91

Inher nherita itance ba nce basi sics: e cs: exte xtended nded I f B inherit s f rom A : � As modules: all t he services of A are available in B (possibly wit h a dif f er ent implement at ion) � As t ypes: whenever an inst ance of A is r equired, an inst ance of B will be accept able (“is-a” relat ionship) I f B inherit s f rom A in a non-conf orming way: � As modules: all t he services of A are available in B (possibly wit h a dif f er ent implement at ion) � No relat ionship bet ween t ypes! 92

Non-confor Non-conformi ming inheritanc ng inheritance class ARRAYED_LI ST [ G ] inherit LI ST [ G ] Non-conf or ming inherit { NONE } inher it ance LI ST ARRAY ARRAY [ G ] ... invariant st ar t s_f r om_1: lower = 1 end ARRAYED_LI ST a : ARRAY [ I NTEGER ]; l : ARRAYED_LI ST [ I NTEGER ] ... Not allowed a := l a.r esize (-10, 10) 93

No n No need for eed for select select Pot ent ial ambiguit y is r esolved is f avor of conf orming parent : count FI NI TE f : FI NI TE [ ... ] al : ARRAYED_LI ST [...] … ARRAY LI ST f := al print ( f . count ) count capacit y ARRAYED_LI ST Ver sion f r om LI ST 94

Covarian Covariance ce class LI ST [ G ] f eature LI ST CURSOR cur sor : CURSOR go_t o ( c: CURSOR ) is do …end … end LI NKED_LI ST LI NKED_CURSOR class LI NKED_LI ST [ G ] inherit LI ST [ G ] redef ine cursor , go_t o, ... end f eature cur sor : LI NKED_CURSOR go_t o ( c: LI NKED_CURSOR ) is do … end … end 95

Anchore Ancho red types d types class LI ST [ G ] f eature cur sor : CURSOR go_t o ( c: like cur sor ) is do …end … end class LI NKED_LI ST [ G ] inherit LI ST [ G ] redef ine cur sor , ... end f eature cur sor : LI NKED_CURSOR -- No need t o redef ine ` go_t o’ … end 96

Sema Semantic ics of an s of anch chore red d ty types pes I n class C : x: SOME_TYPE y : like x I n class C , y is t reat ed exact ly as wit h y: SOME_TYPE I n a descendant D of C , if x has been redeclared t o some ot her t ype, y will be t r eat ed as it if also had t hat t ype. 97

Type re Type redefin definitio ition rule n rule Eif f el: � covar iant redef init ion of result (may change t ype t o a descendant of t he or iginal t ype) � covar iant redef init ion of ar gument s Tradit ional not ion of subt yping : � covar iant redef init ion of result � cont r avar iant redef init ion of argument s (may change t ype t o an ancest or of t he or iginal t ype) Cont ravariant redef init ion: saf e but useless 98

Th The p e pro roblem w blem with th cova variance riance class LI ST f eature list : LI ST [...] cursor: CURSOR go_t o ( c: like cursor ) is do … linked_list : LI NKED_LI ST [...] end … end c : CURSOR class LI NKED_LI ST inherit LI ST … redef ine cursor, ... end f eature list := linked_list cursor: LI NKED_CURSOR list .go_t o (c) -- No need t o redef ine ` go_t o’ … end Cat call! 99

CAT CAT call calls � CAT st ands f or Changing Availabilit y or Type � A rout ine is a CAT if some redef init ion changes it s expor t st at us or t he t ype of any of it s ar gument s � A call is a cat call if some redef init ion of t he rout ine would make it invalid because of a change of export st at us or ar gument t ype 100