Modules in Ruby

A deeper dive than usual

Hal Fulton

June 3, 2019

I wrote one of these books

A module is...

• A tool for namespacing
• A container for methods and constants
• Like a class, but not

A module is
not a class...

• Can't be instantiated

• Has no

• Has no instance variables (of its own)

initialize

What can we do

with a module?

• "nothing" (namespacing)

• include

• extend

• prepend

Namespacing

• Math::PI

• Math::sin

• Math.sin

• ThisClass::SomeModule

• ThisModule::OtherClass

• A::B:C::D::Constant

• A::B::C::D::method

• A::B::C::D.method

"Partial" Multiple Inheritance?

class Asian
end

module Mormon
end

class RubyInventor < Asian
  include Mormon
end

p RubyInventor.ancestors   
# [RubyInventor, Mormon, Asian, Object, Kernel, BasicObject]

matz = RubyInventor.new
p matz.is_a? Asian          # true
p matz.is_a? Mormon         # true

Some core modules

• Comparable           <=>
  

• Enumerable           each
   

                          depends on         
  being implemented

depends on 

• Forwardable

• Math

include

extend

prepend

Manipulating Modules

Copy all constants/methods into a context
(methods go to "current" level)

Copy all constants/methods (methods go in as singletons) -- most commonly used to create class methods

Copy all constants/methods -- methods are given *precedence* over the class's own instance methods!

The Superman example...

ancestors

Idea: Pluggable implementations

I hope this all makes perfect sense.

Questions?