Within Ruby object model, we can include modules. By including a module into a class, we can add instance methods, extend a class with a module, create a namespace with a module, distinguish between prepending modules into classes and including and extending them and use modules to address multiple inheritance in Ruby.
Including Modules
Let's say we have User and Building class. The Postal address is needed for these two classes.
User class
class User
attr_accessor :address_line1, :address_line2, :city, :state,
:postal_code, :country
def mailing_label
label = []
label << address_line1
label << address_line2
label << "#{city}, #{state} #{postal_code}"
label << country
label.join("\n")
end
end
Building class
class Building
attr_accessor :address_line1, :address_line2, :city, :state,
:postal_code, :country
def mailing_label
label = []
label << address_line1
label << address_line2
label << "#{city}, #{state} #{postal_code}"
label << country
label.join("\n")
end
end
With module we can do
module Address
attr_accessor :address_line1, :address_line2, :city, :state
:postal_code, :country
def mailing_label
label = []
label << address_line1
label << address_line2
label << "#{city}, #{state} #{postal_code}"
label << country
label.join("\n")
end
end
class User
include Address
end
class Building
include Address
end
As we can see module are included by module keyword. Classes use it by using include keyword.
Inheritance with Module Methods
When we include a module in a class, we are basically copying the instance methods into a class.
While when a module is extended inside of a class, all of the methods that are defined as basic methods get extended into the class, meaning that they are added as class methods.
- Reference: The Ruby Workshop: Peter Philips && Akshat Paul