Variables in Pharo5
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This document discusses new developments in variable representation in Pharo5. It notes that everything used to be represented as objects, including variables, but variables were represented via associations. In Pharo5, variables are now represented as subclasses of objects called slots and literals. This allows variables to be annotated and have custom behavior via delegation to their metaobjects during code generation. It provides examples of using simple slots, weak slots, and property slots, and outlines the roadmap for further developing the slot system in Pharo6.
Variables in Pharo5
- 1. Variables in Pharo5 ESUG 2015 Marcus Denker http://www.pharo.org
- 2. Everything is an Object
- 3. Everything?
- 5. Methods, yes
- 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
- 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 ?