Ruby: How to access a constant from the class a module is included into

Question

I'm trying to access a constant held within various classes in a module which I am including into them. As a basic example

module foo
  def do_something_to_const
    CONSTANT.each { ... do_something ... }
  end
end

class bar
  include foo

  CONSTANT = %w(I want to be able to access this in foo)
end

class baz
  include foo

  CONSTANT = %w(A different constant to access)
end

As the logic for the module is shared across multiple classes I'd like to be able to just refer to the constant (the name of which stays the same in each class, but the contents vary). How would I go around doing this?

Answer 1

You can reference the class module being included into as self.class and the use const_get or just self.class::CONST, with the latter being slightly faster:

module M
  def foo
    self.class::CONST
  end
end

class A
  CONST = "AAAA"
  include M
end

class B
  CONST = "BBBB"
  include M
end

puts A.new.foo # => AAAA
puts B.new.foo # => BBBB

Answer 2

You can reference the class with self.class

module Foo
  def do_something
    self.class::Constant.each {|x| puts x}
  end
end

class Bar
  include Foo
  Constant = %w(Now is the time for all good men)
end

class Baz
  include Foo
  Constant = %w(to come to the aid of their country)
end

bar = Bar.new
bar.do_something
=>
Now
is
the
time
for
all
good
men
 => ["Now", "is", "the", "time", "for", "all", "good", "men"] 

baz = Baz.new
baz.do_something
=>
to
come
to
the
aid
of
their
country
 => ["to", "come", "to", "the", "aid", "of", "their", "country"]