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rubyclass-variables

Class variables and extending a module

I have a module like the following

module MyModule
  def self.included(base)
    base.extend ClassMethods
  end

  module ClassMethods
    def foo
      @@var = 1
    end

    def bar
      puts @@var
    end
  end
end

class A
  include MyModule
  foo
end

class B < A; end

so that

 B.bar outputs '1'.

However, I would like to have .bar only be defined if .foo is called. I tried

module MyModule
  def self.included(base)
    base.extend ClassMethods
  end

  module ClassMethods
    def foo
      @@var = 1
      extend SingletonMethods
    end

  module SingletonMethods
    def bar
      puts @@var
    end
  end
end

The problem is that

B.bar

returns the error "uninitialized class variable @@var in MyModule::SingletonMethods". How can I make it so that a variable defined in .foo is available to .bar?

Solution

  • use mattr_accessor instead