the best system for object-oriented thinking
TRANSCRIPT
Smalltalk: the best system for
object-oriented *thinking*
http://stephane.ducasse.free.fr http://www.pharo.org
A word of presentation
• Inria research director (was scientific deputee 2011-2014)
• Leads RMOD team (~20 people)
• founder and active developer of Pharo (http://www.pharo.org
• founder of synectique.eu (company)
Reflecting on our daily practice and experience
Properties we see
• Turtles all the way down
• Uniform and elegant
• Simple oo model
• But powerful to build really large applications
• Open system
• Learn from the system itself
What is the essence of OOP?
objects + late binding
objects!
objects!
late binding
Late binding
The fact that the “procedure” to be executed depends on the object on which the computation is requested.
How to convey the object feel?
• Live interaction
• Using Inspectors
• Talk and interact with objects
• Programs are objects too
Scripting livehttps://www.youtube.com/watch?v=1Nze9tnwYxY
http://youtu.be/CuimMwuZiGA
Even with the vocabulary
• We send messages to objects.
• We do not invoke methods!
Sending a message implies looking up for a method
Object
Node
accept:
name
sendt:
node1
msg
Simplicity and elegance
• Syntax fits on a postcard!
• Simple but complete object model
The complete syntaxexampleWithNumber: x “A method that illustrates every part of Smalltalk method syntax”
| y | true & false not & (nil isNil) ifFalse: [self halt]. y := self size + super size. #($a #a ‘a’ 1 1.0)
do: [ :each | Transcript show: (each class name); show: (each printString); show: ‘ ‘].
^ x < y
A Pure OO World
Only objects! mouse, booleans, arrays, numbers, strings, windows, scrollbars, canvas, files, trees, compilers, sound, url, socket, fonts, text, collections, stack, shortcut, streams, …
Less is more!No constructors, no static methods, no operators
No type declaration, no primitive types,
No interfaces, no need for factory
No packages/private/protected modifiers
No parametrized types
No boxing/unboxing
Still powerful
Everything is an object
Objects are instances of Classes
Objects are instances of Classes
!
(10@200)
Objects are instances of Classes
!
(10@200) class
Objects are instances of Classes
!
(10@200) class
Point
Classes are objects too
!
!
Classes are objects too
!
Point selectors
!
!
!
Classes are objects too
!
Point selectors
!
an IdentitySet(#eightNeighbors #+ #isZero #sortsBefore: #degrees #printOn: #sideOf: #fourNeighbors #hash #roundUpTo: #min: #min:max: #max #adaptToCollection:andSend: #quadrantOf: #crossProduct: #= #nearestPointOnLineFrom:to: #bitShiftPoint: #* #guarded #insideTriangle:with:with: #grid: #truncateTo: #y #setR:degrees: #normal #directionToLineFrom:to: #truncated #nearestPointAlongLineFrom:to: #theta #scaleTo: #encodePostscriptOn: #> #asPoint #extent: #r #roundTo: #max: #interpolateTo:at: #triangleArea:with: #angleWith: #dotProduct: #isSelfEvaluating #'<=' #to:intersects:to: #'//' #isInsideCircle:with:with: #< #scaleFrom:to: #corner: #to:sideOf: #x #'>=' #roundDownTo: #onLineFrom:to:within: #transposed #ceiling #angle #basicType #translateBy: #asFloatPoint #'\\' #adaptToNumber:andSend: #abs #negated #octantOf: #asIntegerPoint #flipBy:centerAt: #scaleBy: #floor #onLineFrom:to: #isPoint #reflectedAbout: #/ #dist: #asNonFractionalPoint #bearingToPoint: #reciprocal #rotateBy:centerAt: #rotateBy:about: #rounded #setX:setY: #squaredDistanceTo: #normalized #veryDeepCopyWith: #- #storeOn: #rect: #deepCopy #isIntegerPoint #min #adhereTo: #adaptToString:andSend:)
Classes are objects too
!
Point instVarNames
Classes are objects too
!
Point instVarNames
>#('x' 'y')
Methods are public
Methods are all late-bound
Instance variables are protected
Single Inheritance
Messages + Objects
2 + 5
> 7
Yes + is a message sent to 2
1 class
1 class
> SmallInteger
1 class maxVal
> 1073741823
(1 class maxVal + 1)
(1 class maxVal + 1)
> 1073741824
(1 class maxVal + 1) class
!
(1 class maxVal + 1) class
> LargePositiveInteger
1000 factorial
>
1000 factorial
> 402387260077093773543702433923003985719374864210714632543799910429938512398629020592044208486969404800479988610197196058631666872994808558901323829669944590997424504087073759918823627727188732519779505950995276120874975462497043601418278094646496291056393887437886487337119181045825783647849977012476632889835955735432513185323958463075557409114262417474349347553428646576611667797396668820291207379143853719588249808126867838374559731746136085379534524221586593201928090878297308431392844403281231558611036976801357304216168747609675871348312025478589320767169132448426236131412508780208000261683151027341827977704784635868170164365024153691398281264810213092761244896359928705114964975419909342221566832572080821333186116811553615836546984046708975602900950537616475847728421889679646244945160765353408198901385442487984959953319101723355556602139450399736280750137837615307127761926849034352625200015888535147331611702103968175921510907788019393178114194545257223865541461062892187960223838971476088506276862967146674697562911234082439208160153780889893964518263243671616762179168909779911903754031274622289988005195444414282012187361745992642956581746628302955570299024324153181617210465832036786906117260158783520751516284225540265170483304226143974286933061690897968482590125458327168226458066526769958652682272807075781391858178889652208164348344825993266043367660176999612831860788386150279465955131156552036093988180612138558600301435694527224206344631797460594682573103790084024432438465657245014402821885252470935190620929023136493273497565513958720559654228749774011413346962715422845862377387538230483865688976461927383814900140767310446640259899490222221765904339901886018566526485061799702356193897017860040811889729918311021171229845901641921068884387121855646124960798722908519296819372388642614839657382291123125024186649353143970137428531926649875337218940694281434118520158014123344828015051399694290153483077644569099073152433278288269864602789864321139083506217095002597389863554277196742822248757586765752344220207573630569498825087968928162753848863396909959826280956121450994871701244516461260379029309120889086942028510640182154399457156805941872748998094254742173582401063677404595741785160829230135358081840096996372524230560855903700624271243416909004153690105933983835777939410970027753472000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000
1000 factorial / 999 factorial
1000
1000
Learning from the system…
Three questions
• Question 1: how to implement not
• Question 2: how to implement or or ifTrue:ifFalse:
• Question 3: Why these questions?
Booleans&, |, not, or: ,and:, xor:
ifTrue:ifFalse:, ifFalse:ifTrue:
!
3 > 0
ifTrue: ['positive']
ifFalse: ['negative']
!
-> ‘positive’
!
ifTrue:ifFalse is sent to an object: a boolean!
How to implement not?
• false not -> true
• true not -> false
Let the receiver decide!
Not implementationBoolean>>not
self subclassResponsibility
!
False>>not
^true
!
True>>not
^false
Check in the system
How to implement or?
true | true -> true
true | false -> true
true | anything -> true
!
false | true -> true
false | false -> false
false | anything -> anything
Ok so what?
• You will probably not implement another Boolean classes in your live
• So is it really that totally useless?
!
Message sends act as case statements
!
Message sends act as case statements
• But dynamic and open
• Can add a branch (define a subclass)
• Branches can be defined in different packages
OOP: the art of dispatching
Subclasses create your vocabulary
To be able to select we need classes
Operation1Operation2
AttributeAttribute
Fat ClassClass
OperationA
OperationB'
OperationC'
OperationAttribute
BOperation
C
Vs.
Pharo
http://www.pharo.org
Pure object language
Great community of active doers
Powerful
Elegant and fun to program
Living system under your fingers
A powerful engine to invent (y)our future
An ecosystem where innovation/business bloom
• Uni. of Buenos Aires • Uni. of Bern • Uni. of Maroua • Uni. of Brussels • Ecole des Mines de Douai • Uni. de Savoie • Ivan Franko Nat. Uni. of Lviv • Czech Technical Uni. • CULS Prague• Uni. of Quilmes • Uni. of La Plata • Northern Michigan Uni. • Uni. Technologica Nacional (UTN) • Uni. Catholic of Argentina • Uni. of Santiago • Uni. Policnica de Catalunya • Uni. de Bretagne Occidentale • Uni. of Tomsk • Uni. of Fernhagen • IT University of Copenhagen • Uni. Cat del Sacro Cuore of Brescia
Pharo's Teachers
Lafhis (AR)Software Composition Group (CH) CAR (FR)RMOD (FR) Ummisco (IRD) Reveal (CH) Lysic (FR)Pleiad (CL) CEA-List (FR) Uqbar (AR)
Research Groups
www.2denker.de www.agilitic.com
www.airflowing.com www.anymorphic.com www.ardishealth.com
www.beta9.be www.bombardier.com
www.cmsbox.com www.finworks.biz
seaside.gemstone.com www.ibizlog.com www.inceptive.be www.jooshr.com www.majcon.de
www.mindclue.ch
www.miriamtech.com www.myneat.org www.netstyle.ch
www.panasoft.com www.pinesoft.co.uk
www.promedmedical.net www.sharedlogic.ca
www.smallworks.com.ar www.10pines.com www.trantaria.com www.yesplan.be
www.synectique.eu www.sorabito.com objectprofile.com
!
Companies
BooksPharo by example http://www.pharobyexample.org
translated to french, merci!
translated to spanish, gracias!
translated to japanese, ありがとう!
Deep into Pharo http://www.deepintopharo.org
Numerical Methods
https://github.com/SquareBracketAssociates/NumericalMethods/releases
New books in preparation
Updated Pharo by Example
Entreprise Pharo
Fun with Pharo
www.pharo.org
• Turtles all the way down
• Uniform and elegant
• Simple oo model
• But powerful to build really large applications
• Open system
• Learn from the system itself