whatever.rb

# Looking to write an API like this.
# Before calling Something::Thing#search, there has to be an instance of Something::Connection
# There are other classes to be used that require the connection instance as well.

conn = Something::Connection.new
things = Something::Thing.search('stuff') # requires that an instance of Something::Connection exists
other = Something::Other.stuff('more') # also requires that instance exists
conn.close

# How can I save that instance in such a way that any other classes in that module will see that, 
# without passing that variable every single time?

whoa, thanks @alexpeachey

class Something::Connection
  include Singleton
end

require 'active_support'

class Something::Thing
  cattr_accessor :connection do
    Something::Connection.instance
  end

  def search
    # much better
  end
end

class Something::Other
  cattr_accessor :connection do
    Something::Connection.instance
  end

  def stuff
    # like a lot better
  end
end

I hope this is right