An introduction of the Pharo execution model. Pharo is a new dynamically typed language. It is inspired from Smalltalk and it is elegant, simple and powerful. http://www.pharo.org

1. A Little Journey in the Pharo
Object Model
Stéphane Ducasse
http://www.pharo.org

2. A pure and minimal object model
Less is more!

3. 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

4. Everything is an object

5. Objects are instances of
Classes

6. (10@200)
Objects are instances of
Classes

7. (10@200) class
Objects are instances of
Classes

8. (10@200) class
Point
Objects are instances of
Classes

9. Classes are objects too

10. Point selectors
Classes are objects too

11. 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
Classes are objects too

12. Point instVarNames
Classes are objects too

13. Point instVarNames
>#('x' 'y')
Classes are objects too

14. Methods are public

15. Methods are all late-bound

16. Instance variables are
protected

17. Single Inheritance

18. Object subclass: #Point
instanceVariableNames: 'x y'
classVariableNames: ''
category: 'Graphics-Primitives'
Single Inheritance

19. Messages + Objects

20. Object
Node
accept:
name
sendt:
node1
msg
The key to everything

21. Classes are objects too

22. Point class
Classes are objects too

23. Point class
>Point class
Classes are objects too

24. Point class
>Point class
“Point class” is an anonymous class with only one
instance: Point
Classes are objects too

25. Class Parallel Inheritance
Node class
new
withName: aString
instance of
Node
name
accept: aPacket
send: aPacket
Workstation
originate: aPacket
accept: aPacket
aWorkstation (BigMac)
Workstation
class
instance of

26. Lookup and Class Methods

27. About the Buttons

28. Class methods are plain late
bound methods as any
methods!

29. Package extensions
A method can be defined in a class that
is packaged in another package!
Powerful to build layers

30. Defined in the Dice package
Integer>>D20
^ self D: 20
Integer>>D: anInteger
| h |
h := DiceHandle new
self timesRepeat:
[h addDice: (Dice faces: anInteger)].
^ h
2 D20: two dice of 20 faces

31. Summary
Everything is an object
Single inheritance, public methods,
protected attributes
One single model
Classes are simply objects too
A class is instance of another class
One unique method lookup, look in the
class of the receiver