The best system for object-oriented thinking
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This presentation steps back at our practices and shows why they are successful to immerse people in object-oriented thinking
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The best system for object-oriented thinking
- 1. Smalltalk: the best system for object-oriented *thinking* http://stephane.ducasse.free.fr http://www.pharo.org
- 2. 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)
- 3. Reflecting on our daily practice and experience
- 4. 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
- 5. What is the essence of OOP?
- 6. objects + late binding
- 7. objects!
- 8. objects!
- 9. late binding
- 10. Late binding The fact that the “procedure” to be executed depends on the object on which the computation is requested.
- 11. How to convey the object feel? • Live interaction • Using Inspectors • Talk and interact with objects • Programs are objects too
- 14. Even with the vocabulary • We send messages to objects. • We do not invoke methods!
- 15. Sending a message implies looking up for a method Object Node accept: name sendt: node1 msg
- 16. Simplicity and elegance • Syntax fits on a postcard! • Simple but complete object model
- 17. The complete syntax exampleWithNumber: 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
- 18. 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, …
- 19. 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
- 21. Objects are instances of Classes
- 22. Objects are instances of Classes ! (10@200)
- 23. Objects are instances of Classes ! (10@200) class
- 24. Objects are instances of Classes ! (10@200) class Point
- 25. Classes are objects too ! !
- 26. Classes are objects too ! Point selectors ! ! !
- 27. 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:)
- 28. Classes are objects too ! Point instVarNames
- 29. Classes are objects too ! Point instVarNames >#('x' 'y')
- 31. Methods are all late-bound
- 35. 2 + 5 > 7 Yes + is a message sent to 2
- 36. 1 class
- 38. 1 class maxVal > 1073741823
- 39. (1 class maxVal + 1)
- 40. (1 class maxVal + 1) > 1073741824
- 41. (1 class maxVal + 1) class !
- 42. (1 class maxVal + 1) class > LargePositiveInteger
- 43. 1000 factorial >
- 45. 1000 factorial / 999 factorial
- 46. 1000
- 47. 1000
- 49. Three questions • Question 1: how to implement not • Question 2: how to implement or or ifTrue:ifFalse: • Question 3: Why these questions?
- 50. 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!
- 51. How to implement not? • false not -> true • true not -> false
- 52. Let the receiver decide!
- 53. Not implementation Boolean>>not self subclassResponsibility ! False>>not ^true ! True>>not ^false
- 54. Check in the system
- 55. How to implement or? true | true -> true true | false -> true true | anything -> true ! false | true -> true false | false -> false false | anything -> anything
- 57. Ok so what? • You will probably not implement another Boolean classes in your live • So is it really that totally useless?
- 58. ! Message sends act as case statements
- 59. ! Message sends act as case statements • But dynamic and open • Can add a branch (define a subclass) • Branches can be defined in different packages
- 60. OOP: the art of dispatching Subclasses create your vocabulary
- 61. To be able to select we need classes Operation1 Operation2 Attribute Attribute Fat Class Class Operation A Operation B' Operation C' Operation Attribute B Operation C Vs.
- 62. Pharo http://www.pharo.org Pure object language Great community of active doers Powerful Elegant and fun to program Living system under your fingers
- 63. A powerful engine to invent (y)our future
- 64. An ecosystem where innovation/business bloom
- 65. • 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
- 66. 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
- 68. Books Pharo 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
- 69. 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