Conditional includes

This little problem came up at work a few days ago: what if you want to include a module but, based on the including class, get some different behavior? Enter conditional includes.

module Foo
  module Bar
    def hello
      puts "hi from bar"
    end
  end
  
  module Baz
    def hello
      puts "hi from baz"
    end
  end
  
  def self.included(klass)
    if klass.to_s == "Blah"
      klass.send(:include,Bar)
    else
      klass.send(:include,Baz)
    end
  end
end

Of course, we can change the conditional logic to fit our needs. Now we'll include this module into two classes:

class Blah
  include Foo
end

class Barf
  include Foo
end

Blah.new.hello  # => 'hi from bar'
Barf.new.hello  # => 'hi from baz'

Yahoo! We get different behavior from each class without exposing the complexity to the end user.