import/export in Ruby

bar.rb

ModuleExporter.module(__FILE__) do
  _Bar = Class.new do
    def bar
      "Bar!"
    end
  end

  export _Bar
end

# alternative syntax:
#  export Class.new do
#    def bar
#      "Bar!"
#    end
#  end

foo.rb

ModuleExporter.module __FILE__ do
  # can't use Bar because it's automatically leaking to global namespace
  _Bar = import 'bar' 

  _Foo = Class.new(_Bar) do
    def foo
      "Foo" + bar
    end
  end

  export _Foo
end

module_exporter.rb

class ModuleExporter
  class Sandbox < BasicObject
    def self.import(from)
      ::ModuleExporter.import(from)
    end

    def self.export(object, &block)
      object.class_eval(&block) if block_given?
      @__export__ = object
    end

    def self.__export__
      @__export__
    end
  end

  def self.setup(root:)
    Thread.current['__exports_root__'] = root
    Thread.current['__exports__'] = {}
  end

  def self.root
    Thread.current['__exports_root__']
  end

  def self.module(file, &block)
    Thread.current['__exports__'] ||= {}
    raise 'Only one module block per file!' if Thread.current['__exports__'].has_key?(file)

    Thread.current['__exports__'][file] = Class.new(ModuleExporter::Sandbox)
    Thread.current['__exports__'][file].instance_eval(&block)
  end

  def self.import(source)
    file = File.join(root, source) + ".rb"

    require file unless Thread.current['__exports__'][file]
    raise "Unknown import #{source}. Check your paths (looked in: #{file})" unless Thread.current['__exports__'][file]

    export = Thread.current['__exports__'][file].__export__
    raise "#{source} does not export any classes" unless export

    export
  end
end

test.rb

require './module_exporter'
ModuleExporter.setup(root: File.expand_path(File.dirname(__FILE__)))

_MyLocalClass = ModuleExporter.import 'foo'
MyGlobalClass = ModuleExporter.import 'bar'

puts _MyLocalClass.new.foo # => FooBar!
puts MyGlobalClass.new.bar # => Bar!