Rubyでアノテーションを実装 / Implementing java-like annotations in ruby

annotations.rb

module Annotations
  @@__last_annotation__ = nil

  def annotations(meth=nil)
    return @@__annotations__[meth] if meth
    @@__annotations__
  end

  private

  def singleton_method_added(m)
    (@@__annotations__ ||= {})[m] = @@__last_annotation__ if @@__last_annotation__
    @@__last_annotation__ = nil
    super
  end

  def method_added(m)
    (@@__annotations__ ||= {})["_#{m.to_s}".to_sym] = @@__last_annotation__ if @@__last_annotation__
    @@__last_annotation__ = nil
    super
  end

  def method_missing(meth, *args)
    return super unless /^\_/ =~ meth
    @@__last_annotation__ ||= {}
    @@__last_annotation__[meth[1..-1].to_sym] = args.size == 1 ? args.first : args
  end
end

class Module
  private

  def annotate!
    extend Annotations
  end
end

sample.rb

require './annotations'

class Sample
  annotate!

  _label_only
  def instance_method1; end

  _with_args arg1: 'val1', arg2: 1
  def instance_method2; end

  _label_only
  def self.class_method1; end

  _with_args arg1: 'val2', arg2: 2
  def self.class_method2; end

end

test.rb

require './sample'

p Sample.annotations(:_instance_method1)  # {:label_only=>[]}
p Sample.annotations(:_instance_method2)  # {:with_args=>{:arg1=>"val1", :arg2=>1}}
p Sample.annotations(:class_method1)      # {:label_only=>[]}
p Sample.annotations(:class_method2)      # {:with_args=>{:arg1=>"val2", :arg2=>2}}