Method Shelters : Another Way to Resolve Class Extension Conflicts
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This document discusses method shelters, a new module system for Ruby that aims to resolve conflicts caused by open classes. Method shelters allow defining methods locally within a scope and importing other shelters while preventing conflicts. Key aspects include hidden chambers to protect internally used methods, and a lookup algorithm that prioritizes local shelters over global methods. The implementation adds method shelters as implicit arguments and uses caching to optimize performance. Method shelters can help optimize applications, mimic private variables, and resolve conflicts from open class extensions.
![Refinements
Proposed by Shugo Maeda [ruby-core:33322]
class Foo
module MathN using MathN
refine Fixnum do def foo
def /(other) p1/2
quo(other) end
end end
end
end f = Foo.new
f.foo #=> (1/2)
p1/2](https://image.slidesharecdn.com/rubykaigi11-120203011528-phpapp01/85/Method-Shelters-Another-Way-to-Resolve-Class-Extension-Conflicts-12-320.jpg)
Method Shelters : Another Way to Resolve Class Extension Conflicts
- 1. Method Shelters : Another Way to Resolve Class Extension Conflicts Classboxes でも Refinements でもない別のやり方 Shumpei Akai / 赤井駿平 @flexfrank
- 2. What I talk about today Open Class causes conflicts of methods Method Shelters resolve it!
- 3. % whoami Shumpei Akai / 赤井駿平 @flexfrank Ph.D. Student / 学生(博士課程) ◦ 東工大の千葉研 ◦ Programming Languages and Moduralization ◦ プログラミング言語とモジュール化 Today’s topic is my current research
- 4. Open Class Ruby’s one of the important features You can (re)define methods in existing classes ◦ including Object, Integer, Array, … Frequently used in Ruby world
- 5. in open-uri open-uri redefines “open” method ◦ It accepts URI open("http://penguindrum.jp/"){|f|f.read} # => Errno::ENOENT: No such file or directory require "open-uri” open("http://penguindrum.jp/"){|f|f.read} # => "<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1- transitional.dtd”…”
- 6. in Ruby on Rails ActiveSupport adds various convenient methods to core classes ◦ e.g. 10.megabytes # => 10485760 1.day.ago # => Sat Jul 16 16:15:00 +0900 2011 "survival strategy".pluralize #=> "survival strategies"
- 7. Or Monkey Patching
- 8. Problem of Open Class Methods may conflict When One library adds a method ◦ and another library adds a method with the same name in the same class The method defined first is vanished! ◦ depends on the order of “require” ◦ Confusing!
- 9. Method conflicts I encountered about five years ago ◦ Ruby on Rails and flvtool added a method to String ◦ they used String as binary/array of int Difficult to collaborate these two libraries ◦ I separated processes ◦ communicating via dRuby
- 10. Another example of conflicts “mathn” redefines the “Integer#/” ◦ returns a Rational object ◦ Ordinary code expects “/” returns a integer Programs get broken
- 11. Existing Solutions Several module systems are proposed to resolve conflicts ◦ Selector namespaces (for Smalltalk) ◦ Classboxes (for Smalltalk and Java) ◦ Refinements (for Ruby) ◦ …
- 12. Refinements Proposed by Shugo Maeda [ruby-core:33322] class Foo module MathN using MathN refine Fixnum do def foo def /(other) p1/2 quo(other) end end end end end f = Foo.new f.foo #=> (1/2) p1/2
- 13. Refinements (cont.) Refinements changes behavior of methods in a lexical scope ◦ methods defined by Refinements are not enabled in indirectly called methods ◦ No local rebinding I need local rebinding ◦ e.g. scoped monkey patching
- 14. Classboxes You might have known via matz’s diary
- 15. Classboxes A classbox restrict the scope of methods A classbox can import a class in another classbox ◦ You can use an imported class ◦ You can add/redefine methods to the imported class ◦ A redefined method can be called from the imported class Local rebinding property
- 16. Classboxes Cited from “Classbox/J: Controlling the Scope of Change in Java”
- 17. The Problem in Classboxes Importing overwrites internally used classes ◦ Importing causes another conflict
- 18. The Problem in Classboxes Redefines Original Integer#div Integer Uses redefined Use original Integer#div Integer returns rational Oops! returns integer
- 19. I need another module system A new module should: ◦ have local rebinding ◦ provide a way to resolve conflicts cause by importing ◦ not depends on the order of load
- 20. Method Shelters
- 21. Key concept Hide your methods Hide your imports
- 22. What is a method shelter A method shelter is a module which provides a scope of methods ◦ define methods in a method shelter ◦ import other method shelters You can call methods in the imported shelter You can call methods in the shelter which is importing the current shelter for local rebinding call importee call importer
- 23. A Code with Method Shelters shelter :MathN do class Fixnum # fixed size integer in Ruby def /(x) Rational(self,x) end end end shelter :Average do class Array def avg sum = self.inject(0){|r,i|r+i} sum / self.size end end hide import :MathN end
- 24. What conforms a method shelter A method shelter is separated into tow parts ◦ An exposed chamber and a hidden chamber ◦ in order to protect internally used methods ◦ Each chamber can define methods and import - Exposed - Hidden
- 25. Exposed Chambers S0 - Obj#m0 for public API Exposed methods ◦ Visible from importer ◦ Importer can call or redefine exposed S1 methods Exposedly import ◦ Transitive importing ◦ Imported methods are S2 also visible from importer
- 26. Hidden chamber S0 - Obj#m1 - Obj#m0 for internally used methods Hidden method S1 ◦ invisible in importing shelter Hiddenly import S2 ◦ Imported methods are not exposed
- 27. Global Methods Ordinal methods not in shelters ◦ Callable from any shelter ◦ Global methods can call methods in a shelter if the caller is in the shelter Global - Obj#g0 S0 obj.g0()
- 28. No Ambiguity If 2+ methods are found in imported shelters S3 - C#m0 ◦ Error! S1 S2 - C#m0 S0 Error!
- 29. Syntax I don’t want to edit parse.y define methods in a block shelter :ShelterName do class Foo def hoge # <- defined in the method shelter end end end
- 30. Syntax: Import shelter :ShelterName do import :AnotherShelterName end
- 31. Syntax: hide “hide” method switches a chamber ◦ do def or import below “hide” shelter :ShelterName do # exposed chamber hide # hidden chamber end
- 32. Evaluate Evaluate within a shelter shelter_eval :ShelterName do #shelter is enabled end
- 33. Method Lookup Algorithm 1. look up hidden-chamber 2. look up exposed-chamber 3. look up global methods If not found, go to superclass
- 34. 8 3 7 6 2 5 1 start Global 9 4
- 35. Found! 1 Start Global
- 36. Implementation Based on Ruby 1.9.2 Add one implicit argument to method: ◦ A node of method shelter tree
- 37. Optimization: Method Cache Shelter node cache ◦ Caches method entry in a node of shelter Extend inline cache ◦ Size of an inline cache : 3 word -> 4word (per method call) ◦ Stores the found shelter node
- 38. Performance: empty methods Call a empty method 10,000,000 times ◦ Less than 5% overhead when shelters are used
- 39. Performance: Fibonacci fib(33) in a method shelter ◦ Up to 20% overhead
- 40. Performance: Ruby on Rails Enabled in an action method ◦ Numeric#/.*bytes?/ methods are in a shelter In the action ◦ 1. Call one method in shelter ◦ 2. One access to SQLite via ActiveRecord on WEBRick Rails3
- 41. Performance: Ruby on Rails (result) 4% overhead on production env. 50% on development ◦ Method caches are invalidated per req. production development
- 42. Cache hit ratio on rails Count shelter’s cache hit
- 43. Performance: tDiary 3.0.1 defined String#to_a, String#each, String#method_ missing in a shelter ◦ These are used for compatibility of 1.8 & 1.9 Ran on CGI with apache Method shelter improved performance !! ◦ Why?
- 44. Why shelter made tDiary fast String#method_missing issue “require” calls its arg’s to_path method if defined ◦ If arg’s method_missing is defined, try to call it ◦ String#method_missing slows “require” Method shelter restrict its negative effect
- 45. Other Usage: protect optimized methods In ruby, + - * / … are optimized ◦ only if they are not redefined ◦ Redefinition slows programs Method shelters can confine effect of redefinition Method shelter can improve performance
- 46. Other Usage: shelter-private accessor Ruby has no private instance variables A method shelter can mimic private ivars ◦ by generating unique name ◦ Accessible within the defined shelter and visible shelters
- 47. class Module def shelter_accessor(name) define_method name do ivname=get_unique_name(name) self.instance_variable_get(ivname) end define_method( (name.to_s+"=").to_sym) do|val| ivname= get_unique_name(name) self.instance_variable_set(ivname,val) end end end
- 48. Conclusion Open class is dangerous Method shelters resolving conflicts ◦ With hidden methods, hiddenly importing I implemented in Ruby ◦ Not so slow (個人的な感覚) For more details or the source code, ◦ wait for the acceptance of my paper Deadline: 2.days.since
- 49. Questions?
- 50. 時間が余ったら
- 51. Global
- 52. In my lookup algorithm, ◦ Shelter must have up to one parent For simpler semantics For efficient implementation
- 53. before C B A
- 54. after C’ C’’ B A