# lib/rspec/core/subject.rb

require 'ostruct'

def its(attribute, &block)
  describe(attribute) do
    example do
      self.class.class_eval do
        define_method(:subject) do
          attribute.to_s.split('.').inject(super()) do |target, method|
            target = OpenStruct.new(target) if target.is_a?(Hash) && attribute.is_a?(Array)
            target.send(method)
          end
        end
      end
      instance_eval(&block)
    end
  end
end

# spec/rspec/core/example_group_spec.rb

context "when it's a Hash" do
  subject do
    { :attribute => 'value',
      'another_attribute' => 'another_value'}
  end
  its([:attribute]) { should == 'value' }
  its([:another_attribute]) { should == 'another_value' }
  its(:keys) { should == ['another_attribute', :attribute] }

  context "when referring to an attribute without the proper array syntax" do
    it "raises a NoMethodError" do
      expect{ its(:attribute) }.to raise_error(NoMethodError)
    end
  end

end