Include vs Extend

  • Include is for adding methods only to an instance of a class

    • instance methods. Without self.

  • Extend is for adding methods to the class but not to its instance.

    • class methods. With self.

Include - To the instance#

module Animal
def eat
p "I eat"
end
end
class Dog
include Animal
def bark
p "I bark"
end
end
dog = Dog.new
dog.eat
# Output:
$ruby main.rb
"I eat"

Include can't use class methods:#

module Animal
def self.eat
p "I eat"
end
end
class Dog
include Animal
def bark
p "I bark"
end
end
dog = Dog.new
dog.eat
# Output:
$ruby main.rb
main.rb:15:in `<main>': undefined method `eat' for #<Dog:0x00556724be0bf0> (NoMethodError)

Extend : Imports as class method:#

module Animal
def eat
p "I eat"
end
end
class Dog
extend Animal
def bark
p "I bark"
end
end
Dog.eat
# Output:
$ruby main.rb
"I eat"

Extend: can't call class methods from Module:#

module Animal
def self.eat
p "I eat"
end
end
class Dog
extend Animal
def bark
p "I bark"
end
end
Dog.eat
# Output:
$ruby main.rb
main.rb:14:in `<main>': undefined method `eat' for Dog:Class (NoMethodError)
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