The document discusses the implementation of variables in Pharo 5, highlighting that everything in the system is treated as an object, including variables, class variables, and global variables. It details how the Opal compiler integrates with variable management, including reflective reading and writing of variables, and outlines a roadmap for future enhancements in handling slots and variable types. The content emphasizes collaborative work and contributions from several individuals in the development of these features.

1. Variables in Pharo5
ESUG 2015
Marcus Denker
http://www.pharo.org

2. Everything is an Object

3. Everything?

4. Classes, yes.

5. Methods, yes

6. But Variables?

7. Everything is an object?
SmalltalkImage classVarNamed: #CompilerClass
==> returns value
Object binding class
==> Association

8. Why not an Object?

9. Globals/ClassVariables
• We are close: bindings are associations
• Add sublass “LiteralVariable”
• Sublasses GlobalVariable, ClassVariable
• Enhance API

10. Globals/ClassVariables
SmalltalkImage classVariableNamed: #CompilerClass
Object binding class

11. Globals: Reflective APi
global := SmalltalkImage classVariableNamed:
#CompilerClass
global read
global write: someObject
+ helper methods + compatibility methods

12. Everything is an object?
• Point instanceVariables
• 5@3 instVarNamed: ‘x’
• 5@3 instVarNamed: ‘y’ put: 6

13. Why not an Object?

14. Slots
Point slots
(Point slotNamed: #x) read: (3@4)
(Point slotNamed: #x) write: 7 to: (3@4)

15. Variables+MetaLink
• Helper methods
• But: can’t we annotate variables directly?
Point assignmentNodes

16. Variables + Links
• Object binding link: myMetaLink
• (Point slotNamed: #x) link: myMetaLink
(not yet in Pharo5)

17. Opal Compiler
• Uses RB AST
• Based on Visitors
Text AST
AST
+vars
IR CM
Parser Semantic
Analysis
AST Translator+
IRBuilder
BytecodeBuilder+
Encoder

18. Opal Compiler
• Name analysis finds the variables
• Code generator can delegate to them
Text AST
AST
+vars
IR CM
Parser Semantic
Analysis
AST Translator+
IRBuilder
BytecodeBuilder+
Encoder

19. Gobals: code read
• By default compile reflective read
emitValue: aMethodBuilder
aMethodBuilder
pushLiteralVariable: #slot->self;
send: #read

20. Gobals: code write
• By default compile reflective write
emitStore: aMethodBuilder
| tempName |
tempName := Object new.
aMethodBuilder
addTemp: tempName;
storeTemp: tempName;
popTop;
pushLiteralVariable: #global -> self;
pushTemp: tempName;
send: #write:

21. Gobals: code write
• ClassVariable and GlobalVariable override
emitStore: methodBuilder
methodBuilder storeIntoLiteralVariable: self.

22. Same for Slots
• Slot generates reflective read/write
• InstanceVariableSlot overrides for fast instance
access via byte code

23. What does that mean?
• Slots and Globals are instances of a class
• The compiler delegates code generation to the
variable meta object
• Which means: We can define our own variables!

24. Class Template
Object subclass: #Point
slots: { #x. #y }
classVariables: { }
category: 'Kernel-BasicObjects'

25. Class Template
Object subclass: #MyClass
slots: { #x => WeakSlot }
classVariables: { }
category: 'Example'

26. Examples: DEMO
• Simple Slot
• WeakSlot
• Property Slot
• Boolean

27. RoadMap
• Pharo3:
• Layout+Slots (hidden), Opal
• Pharo4
• Slots: Monticello support, class template
• Pharo5
• Remove old Compiler/AST
• Slots + Reflectivity: First finished version

28. RoadMap
• Pharo6:
• Library of useful Slots
• Use e.g. Property Slots in Bloc/Morphic

29. Future
• Can’t we model bit patterns and bind them to
named virtual slots?
• How to model Array-like layouts better?

30. Thanks!
• Work of many people…
• special thanks to… Toon Verwaest, Camillo
Bruni, Martin Dias, Stephane Ducasse, Max
Mattone and Camille Teruel

31. Questions ?