Ruby Object Model

WarmUp

• What’s the difference between a class and an instance from Ruby’s perspective?
• How are modules used as “mix-ins”?
• How do you know what variables, methods and classes you have available at any given time?

Investigative Methods

• .ancestors
• .included_modules
• .superclass

Mapping Ruby’s Object Model

Definitions and Rules

• Classes: store instance methods, have a superclass pointer
• Instances: store instance variables, have a class pointer
• Classes are also instances (of Class)
• Classes can only inherit from one other class (its ‘superclass’)
• Classes can include multiple Modules.
• Modules can be mixed-in to multiple classes (mixins)

Exercises

Use .class, .ancestors, .included_modules, and .superclass to diagram the lookup chain of the following Ruby classes:

• Hash
• Array
• String
• Integer
• Float

Share

Scope with Variables & Methods

• See lesson plan for code

Practice

When I call Chair.new.chair_type what will be my output? How could I get it to print module? How could I get Chair.new.chair_type to print method? How could I get Chair.new.chair_type to print superclass? How could I get Chair.new.chair_type to print superclass's superclass?

Lookup Chain

• Start by looking for a local variable
• Check its class for a method
• Look to that class’s included_modules
• Until it finds the method, go to the superclass
• Once you find it, create a scope for that object

Bindings

• When a scope is created, it’s called a Binding.
• Binding: a Ruby class that captures the context in which code is executed.
• The binding retains the context for future use, including
  • relevant variables
  • methods
  • the value of self
  • some other contextual details

Explore

• See lesson plan.

WrapUp

• How does Ruby’s look up chain work? What is the order it checks things?
• What are three methods you can use to learn about where a built in Ruby method gets its components?
• Draw a diagram of where Ruby would look for the method ::new
• What is a binding?