Question

I’m confused with Ruby’s attr_writer.
I’m trying to add a value inside an array but i’m encountering the following error:

Line 13: undefined method `test’ for # (NoMethodError)

class Pet
  attr_writer :test
  def initialize()
    @test = []
  end
end

pet = Pet.new()
pet.test << "Test was a pet"

Why? As I understand it, attr_writer is equivalent to a setter method.
Please explain. Thank you.

Answer 1

Yes, attr_writer defines a setter method. But your code tries to use a getter

pet.test << "Test was a pet"

Here’s how ruby sees it (more or less)

t = pet.test
t << "Test was a pet"

If you actually set an array, it will work

pet.test = ['Test was a pet']

As a side note: I personally consider write-only properties as a code smell. Something is probably wrong here. I have never had to use write-only attributes in my career.