Let’s learn about singleton_class with an example. I have a Car which knows to drive.
class Car
def drive
puts "I am driving"
end
end
car = Car.new
car.drive # I am driving
Cool so what! Now at later point of time I want to add honk to my car only when it is stuck in traffic. I don’t want it to be added for every Car object.
There might be more than one way of doing this in ruby but in the interest of this post i will implement this with singleton_class. Ruby singleton_class inserts a new anonymous class into the inheritance hierarchy as a container and adds the new method to it.
class Car
def drive
puts "I am driving"
end
end
module Honking
def honk
puts "Get away on my way"
end
end
car = Car.new
traffic = true # more logic here
if traffic
car.singleton_class.include(Honking)
end
car.honk
p car.singleton_methods # [:honk]
race_car = Car.new
race_car.honk # undefined method `honk'
singleton_class creates a new singleton class if car does not have one. From then what ever changes you make on that is going to be affected to that particular class. Thats the reason race_car doesn’t know anything about honk.
I also used singleton_classto add additional validations to the object in a specific context.
You can check singleton methods on a class using singleton_methods.
Happy coding!
