Problem with Rails autoload and classes used for directory namespacing

rails_autoload_issue.rb

# If you have the following setup, Rails autoload will depend on load order in a hard-to-trace way:

# app/models/foo.rb
class Foo
  def initialize(arg)
    @arg = arg
  end
end

# app/models/foo/bar.rb
class Foo
  class Bar
  end
end

require 'foo/bar'
Foo.new('hello') # => wrong number of arguments (1 for 0)

# Rails already registered definition of Foo in file foo/bar.rb, which didn't have initialize.
# So it assumes that class Foo is already loaded, and has empty initialize. You get wrong number of args error.

# If you change app/models/foo/bar.rb to this:
class Foo::Bar
end

# Then this works:
require 'foo/bar'
Foo.new('hello') # => <Foo>
# because in this case the Foo inside foo/bar.rb was a mention, not a definition.
# Rails will go ahead and try to find the actual definition in foo.rb.