Ruby object graph
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This document discusses Ruby object graphs and relationships between objects, classes, modules, and singletons in Ruby. It covers how Ruby determines where to look for methods and attributes based on an object's class and inheritance hierarchy. It also describes how to define singleton methods on a specific object, class methods, extending and including modules to add methods to objects and classes in Ruby.
Ruby object graph
- 1. Ruby Object Graphs Avilay Parekh
- 2. Conventions object Derived Base object, Base, and Derived are all Ruby objects. object’s class is Derived. Derived is a subclass of Base.
- 3. Calling Scope c1 @flavor = ‘choc’ @calories = 100 Cookie flavor=() flavor () Class - new() Snack calories=() calories() Module Object BasicObject class Snack def initialize @calories = 100 end end class Cookie < Snack def initialize @flavor = „choc‟ end end c1 = Cookie.new c1.calories looks in this hierarchy. Cookie.new looks in this hierarchy. For obj.method Ruby will look in the hierarchy pointed to by obj’s class. For method Ruby will look in the hierarchy pointed to by self’s class For @attribute Ruby will look for the attribute in self.
- 4. Singletons c1 Class Define methods on a specific object that will be available to only that object and no other object. Not the same as the singleton creation design pattern! This is done by “inserting” an anonymous class at the end of the object’s class hierarchy. Note, the picture below does not show the usual Module, Object, BasicObject, etc. class Cookie # same as before end c1 = Cookie.new def c1.eat puts “chomp..chomp” end c2 = Cookie.new c1.eat # => “chomp..chomp” c2.eat # => no method found Anon -eat() Cookie Snack
- 5. Class Methods c1 Class Known as “static methods” in C#. Simply a special case of singletons described in the previous slide. An anonymous class is inserted at the end of Cookie’s class hierarchy. Anon -sweet?() Cookie Snack class Cookie # same as before def Cookie.sweet? true end end puts Cookie.sweet?
- 6. class Cookie # same as before end c1 = Cookie.new def c1.eat puts “chomp..chomp” end class << c1 def munch puts “yummy!” end end c1.eat c1.munch Another way to define singletons Singletons class Cookie # same as before def Cookie.sweet? true end class << self def savory? false end end end puts Cookie.sweet? puts Cookie.savory?
- 7. extend object with Module c1 Class Instance methods of the module are available as instance methods of that specific object. Like singleton methods, except loosely coupled. Anon class points to the Module’s method table instead of having the methods itself. Done by “including” the module in a newly created singleton class. Anon Cookie Snack module Recipe def slice :: end end class Cookie < Snack # same as before End c1 = Cookie.new c1.extend Recipe c1.slice Recipe -slice methods
- 8. extend class with Module c1 Instance methods of the module are available as class methods of the class. Like class methods, except loosely coupled. Cookie Snack module Recipe def slice :: end end class Cookie extend Recipe end Cookie.slice Anon Recipe -slice methods Class
- 9. include Module in class c1 Class Instance methods of the module are available as instance methods of the class. Like OO inheritance, except loosely coupled. Done by “inserting” an anonymous class in the middle of the object’s class hierarchy. Cookie Snack Anon Recipe -slice methods module Recipe def slice :: end end class Cookie < Snack include Recipe # same as before End c1 = Cookie.new c1.slice c1.flavor