Calling a method without an instance

Question

I have the following code:

class Cars
  attr_accessor :car_make
  attr_accessor :car_model
  def initialize(make, model)
    self.car_make = make
    self.car_model = model
  end
end

I would like to know if it is possible to implement a list_cars method and call the method like so:

ford = Cars.new("Ford" ,"F-150")
honda = Cars.new("Honda", "CRV")
list_cars(ford, honda)

i.e., without necessarily calling it from an existing object. I tried this:

def list_cars(first_car, second_car)
  puts "My father has two cars - a #{first_car.car_make} #{first_car.car_model} and a #{second_car.car_make} #{second_car.car_model}."
end

I realize that this code is missing something, but I don't know what that is.

undefined method `list_cars' for main:Object (NoMethodError) — skwidbreth
– skwidbreth, Commented Dec 5, 2015 at 15:35
list_cars is implemented outside class Cars right? Your code works for me. — rohit89
– rohit89, Commented Dec 5, 2015 at 15:38

Markus · Accepted Answer · 2015-12-05 15:44:10Z

2

Make it a class method:

class Cars
  def self.list_cars(first_car, second_car)
    puts "My father has two cars - a #{first_car.car_make} #{first_car.car_model} and a #{second_car.car_make} #{second_car.car_model}."
  end
end

Then you can call it simply by:

Cars.list_cars(car1, car2)

You can find more about class methods at rubymonk.

If this is the right way (or a new module, or as a method in object space) depends on your project architecture.

answered Dec 5, 2015 at 15:44

Markus

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1 Comment

skwidbreth Over a year ago

Ah perfect, that does it. Thanks for the tip on the resource, too - I'm teaching myself...

sawa · Accepted Answer · 2015-12-05 15:58:15Z

1

Markus's answer is the way people would normally do (and can be the preferred way since that would not pollute the main namespace). But that is not a solution to what you want. In order to do that you want, you usually implement the method on Kernel.

module Kernel
  def list_cars(first_car, second_car)
    puts "My father has two cars - a #{first_car.car_make} #{first_car.car_model} and a #{second_car.car_make} #{second_car.car_model}."
  end
end

answered Dec 5, 2015 at 15:58

sawa

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