Question

I’m writing a program like this:

module Filter
  def self.included?(klass)
    @count = 0
  end
end

class Object
  include Filter
end

class Person
  def get_count
    puts @count
  end
end

I want to define an instance variable @count through mixing Filter, hoping this mixin is accessible to all the Object.

However, my way doesn’t work.

Can anyone tell me how to achieve this?

Answer 1

Don’t use a variable, use an attribute:

module Counter
  attr_accessor :count
end

class Person
  include Counter
end

person = Person.new
person.count = 50
puts person.count

Also, don’t include stuff into Object, only include in your classes. Polluting the main namespace with non-general methods is bad and could lead to method name clashes in other classes, causing hard-to-find bugs.

Only include modules where you think they’re needed, not everywhere.