First class Variables in Pharo
- 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 ?