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PHP Traits: Horizontal Reuse of Behavior
- 1. PHP.next: Traits Horizontal Reuse of Behavior Stefan Marr AFUP, La Can@ne, Paris 15th December 2010
- 2. Ques@ons at any @me
- 3. Traits for PHP Started December 2007 15/12/10 3
- 4. Today: Virtual Machines for the Manycore Era hOp://soR.vub.ac.be/~smarr/research/ hOp://github.com/smarr/RoarVM 15/12/10 4
- 5. Who are you? • PHP Programmer: Job or Hobby? • C Programmer? (PHP core/extensions?) • Contribu@on to Open Source projects? 15/12/10 5
- 6. Off-‐Topic… Anyone using: • COCOMO, COCOMO II • Func@on points • User Story Points 15/12/10 6
- 7. Ques@ons at any @me
- 8. Agenda • Why Traits? • The Language Design • Traits Applied • Implementa@on inside the Zend Engine 15/12/10 8
- 9. Reuse in Programming Languages WHY TRAITS? 15/12/10 Stefan Marr – PHP.next: Traits 9
- 10. Single Inheritance Vertebrates • Simple but not expressive enough • Leads to Dinosaurs Mammal • Code duplica@on • Inappropriate hierarchies Archaeoptrix Bat fly() fly() 15/12/10 Approaches for ComposiIon and their Limits 10
- 11. Mul@ple Inheritance Animal • Very expressive +move() • But Bird Swimmer • Diamond problem +move() +move() • Fragile hierarchies +getLegs() Penguin class Penguin { function move() { +move() Swimmer::move(); } } 15/12/10 Approaches for ComposiIon and their Limits 11
- 12. Mixins Animal WingAnimal <<mixin>> (1) Bat <<mixin>> (1) bones = light extremity = wings Penguin move() <<mixin>> (2) SwimAnimal extremity = fins move() 15/12/10 Approaches for ComposiIon and their Limits 12
- 13. Mixins Animal WingAnimal <<mixin>> (1) Bat <<mixin>> (1) bones = light extremity = wings Penguin move() <<mixin>> (2) SwimAnimal extremity = fins • Lack of composi@on move() control • Fragile hierarchies 15/12/10 Approaches for ComposiIon and their Limits 13
- 14. Limita@ons • Code duplica@on • Inappropriate hierarchies • Diamond problem • Fragile hierarchies • Lack of composi@on control 15/12/10 Approaches for ComposiIon and their Limits 14
- 15. Traits for PHP THE LANGUAGE DESIGN 15/12/10 Stefan Marr – PHP.next: Traits 15
- 16. Traits • Set of methods • Possibly composed of other Traits • Composi@on is unordered TFoo • Composi@on opera@ons TTrait foo() TBar – Sum m1() m2() bar() MyClass – Exclusion TConflict – Aliasing m2() • Can be flaOened away 15/12/10 Traits 16
- 17. Traits in Ac@on 15/12/10 Traits 17
- 18. Method in Class Overrides Trait Base foo() class Base { Code function foo() { echo 'B';}} A T foo() foo() trait T { function foo() { echo 'T';}} Base Compiled Result foo() class A extends Base { use T; function foo() { echo 'A';}} A foo() echo 'A'; 15/12/10 Traits 18
- 19. Conflicts are Explicit Base class Base { foo() function foo() { echo 'B';}} T1 Code foo() trait T1 { A function foo() {echo 'T1';}} T2 foo() trait T2 { Base function foo() {echo 'T2';}} Compiled Result foo() class A extends Base { use T1, T2; A >> Fatal error: } collision on foo 15/12/10 Traits 19
- 20. Solving Conflicts Base class Base { foo() function foo() { echo 'B';}} T1 trait T1 { Code foo() function foo() {echo 'T1';}} A trait T2 { T2 function foo() {echo 'T2';}} !foo foo() Base class A extends Base { Compiled Result foo() use T1, T2 { T1::foo insteadof T2; } A } foo() >> echo 'T1'; 15/12/10 Traits 20
- 21. Aliasing Base class Base { foo() function foo() { echo 'B';}} T1 trait T1 { Code foo() function foo() {echo 'T1';}} A trait T2 { !foo T2 function foo() {echo 'T2';}} +foo2 foo() Base class A extends Base { Compiled Result foo() use T1, T2 { T1::foo insteadof T2; T2::foo as fooT2; A foo() >> echo 'T1'; } foo2() >> echo 'T2'; } 15/12/10 Traits 21
- 22. Aliasing IS NOT Renaming trait T1 { class A { function bar() { echo 'T1::bar'; use T1, T2 { } T2::bar insteadof T1; function foo() { T1::bar as bar2; $this-‐>bar(); } } } } trait T2 { function bar() { $a = new A; echo 'T2::bar’; } $a-‐>foo(); // echo ?? } 15/12/10 Traits 22
- 23. Late Binding for Composability trait MovingAnimal { class Penguin { function move() { use WingAnimal, SwimAnimal { $this-‐>extremities()-‐>use(); WingAnimal::extremities }} insteadof SwimAnimal; trait WingAnimal { } use MovingAnimal; } function extremities() { return $this-‐>wings; $skipper = new Penguin; }} $skipper-‐>move(); // will use trait SwimAnimal { his wings use MovingAnimal; function extremities() { return $this-‐>fins; }} 15/12/10 Traits 23
- 24. Traits and State trait Counter { abstract function &getValueVar(); function inc($inc = 1) { $var = &$this-‐>getValueVar(); $var = $var + $inc; }} class PageWithCounter { use Counter; public $counter = 1; function &getValueVar() { return $this-‐>counter; } } $page = new PageWithCounter; $page-‐>inc(); var_dump($page-‐>counter); 15/12/10 Traits 24
- 25. Case Studies Illustra@ng Benefits of Traits TRAITS APPLIED 15/12/10 Stefan Marr – PHP.next: Traits 25
- 26. Use Case for Traits • ezcReflec@on enhances PHP Reflec@on API – Adds XDoclet like annota@ons for PHP – Enhances type hin@ng using PHPDoc type annota@ons • Illustrates solu@on for code duplica@on problems «interface» Reflector ReflectionProperty ReflectionClass ReflectionFunction ReflectionParameter ReflectionObject ReflectionMethod 15/12/10 Traits Applied 26
- 27. Refactoring ezcReflec@on with Traits 15/12/10 Traits Applied 27
- 28. Refactoring ezcReflec@on with Traits 15/12/10 Traits Applied 28
- 29. Implementa@on details: Not to be confused with language seman@cs! The Traits Implementa@on INSIDE THE ZEND ENGINE 15/12/10 Stefan Marr – PHP.next: Traits 29
- 30. Zend Engine Overview PHP + Zend Engine YACC Opcodes Script Parser Structures Opcode Interpreter Result Input Input 15/12/10 Traits inside the Zend Engine 30
- 31. YACC Parser Parser • Added keywords – trait – insteadof • Grammar rules based on class 15/12/10 Traits inside the Zend Engine 31
- 32. PHP + Zend Engine Zend Engine • Trait internally a class with ZEND_ACC_TRAIT – New data structures • zend_trait_method_reference • zend_trait_precedence • zend_trait_alias – Class members added to zend_class_entry • zend_class_entry **traits; • zend_uint num_traits; • zend_trait_alias **trait_aliases; • zend_trait_precedence **trait_precedences; • Support in Reflec@on API 15/12/10 Traits inside the Zend Engine 32
- 33. Opcode Interpreter Interpreter • Added Opcodes – ZEND_ADD_TRAIT • similar to ZEND_ADD_INTERFACE • Only adds info, no composi@on done – ZEND_BIND_TRAITS • emiOed in zend_do_end_class_declara@on • will ini@ate trait composi@on at run@me – Only once, part of class defini@on process – (no run@me overhead) 15/12/10 Traits inside the Zend Engine 33
- 34. PHP + Zend Engine Composi@on Process • Implemented in zend_do_bind_traits 1. Init traits data structures (resolve classes) 2. For all used traits – Compile method table of all used methods – Respect exclusion and aliases 3. Merge resul@ng tables 4. Add methods to class – Handle abstract methods, inheritance – duplicate func@on (like copy/paste, enables static) 15/12/10 Traits inside the Zend Engine 34
- 35. ROUNDUP AND CONCLUSION 15/12/10 Stefan Marr – PHP.next: Traits 35
- 36. References for Traits in PHP RFC: Horizontal Reuse in PHP Version 2.0.1, last update 2010-‐11-‐18 hOp://wiki.php.net/rfc/horizontalreuse Interes@ng Blog Posts – Simas Toleikis: Overview, similar to RFC • hOp://simas.posterous.com/new-‐to-‐php-‐54-‐traits – Sebas@an Deutsch: Ac@veRecord with Traits • hOp://9elements.com/io/?p=28 15/12/10 Roundup and Conclusion 36
- 37. Conclusion • Traits are mechanism for reuse of behavior • Avoid limita@ons of other approaches – Avoid code duplica@on – Enhance class composi@on capabili@es • “Compiler assisted copy’n’paste” – FlaOened into class – No run@me overhead 15/12/10 Roundup and Conclusion 37
- 38. Basic Literature on Traits Main ArIcle about Traits [3] S. DUCASSE, O. NIERSTRASZ, N. SCHÄRLI, R. WUYTS, AND A. P. BLACK, Traits: A Mechanism for Fine-‐Grained Reuse, ACM Trans. Program. Lang. Syst., 28 (2006), pp. 331–388. Traits Extensions [1] A. BERGEL, S. DUCASSE, O. NIERSTRASZ, AND R. WUYTS, Stateful Traits and their Formaliza;on, Journal of Computer Languages, Systems and Structures, 34 (2007), pp. 83–108. [4] S. DUCASSE, R. WUYTS, A. BERGEL, AND O. NIERSTRASZ, User-‐Changeable Visibility: Resolving Unan;cipated Name Clashes in Traits, SIGPLAN Not., 42 (2007), pp. 171–190. 15/12/10 Roundup and Conclusion 38
- 39. Traits Literature [1]A. BERGEL, S. DUCASSE, O. NIERSTRASZ, AND R. WUYTS, Stateful Traits and their Formaliza;on, Journal of Computer Languages, Systems and Structures, 34 (2007), pp. 83–108. [2]S. DENIER, Traits Programming with AspectJ, RSTI -‐ L'objet, 11 (2005), pp. 69–86. [3]S. DUCASSE, O. NIERSTRASZ, N. SCHÄRLI, R. WUYTS, AND A. P. BLACK, Traits: A Mechanism for Fine-‐Grained Reuse, ACM Trans. Program. Lang. Syst., 28 (2006), pp. 331–388. [4]S. DUCASSE, R. WUYTS, A. BERGEL, AND O. NIERSTRASZ, User-‐Changeable Visibility: Resolving Unan;cipated Name Clashes in Traits, SIGPLAN Not., 42 (2007), pp. 171– 190. [5]S. MARR AND F. MENGE, ezcReflec;on, SVN Repository, eZ Components, January 2008. hOp://svn.ez.no/svn/ezcomponents/experimental/Reflec@on. [6]E. R. MURPHY-‐HILL, P. J. QUITSLUND, AND A. P. BLACK, Removing Duplica;on from java.io: a Case Study using Traits, in OOPSLA '05: Companion to the 20th annual ACM SIGPLAN conference on Object-‐oriented programming, systems, languages, and applica@ons, New York, NY, USA, 2005, ACM, pp. 282–291. 15/12/10 Roundup and Conclusion 39
- 40. Traits Literature [7] PROGRAMMING METHODS LABORATORY, Traits for Scala, Programming Language, Ecole Polytechnique Fédérale de Lausanne, 2006. hOp:// www.scala-‐lang.org/intro/traits.html. [8] P. J. QUITSLUND, E. R. MURPHY-‐HILL, AND A. P. BLACK, Suppor;ng Java traits in Eclipse, in eclipse '04: Proceedings of the 2004 OOPSLA workshop on eclipse technology eXchange, New York, NY, USA, 2004, ACM, pp. 37–41. [9] S. REICHHART, Traits in C#. Video of Talk at MicrosoR Research, September 2005. [10] N. SCHÄRLI, Traits — Composing Classes from Behavioral Building Blocks, PhD thesis, University of Berne, Feb. 2005. [11] SOFTWARE COMPOSITION GROUP, Traits for Squeak, Smalltalk VM, University of Berne, December 2006. hOp://www.iam.unibe.ch/ scg/Research/ Traits/index.html. [12] L. WALL, Apocalypse 12: Class Composi;on with Roles, tech. report, The Perl Founda@on, 2004. hOp://www.perl.com/pub/a/2004/04/16/ a12.html?page=11. 15/12/10 Roundup and Conclusion 40