Ruby Refinements

gistfile1.rb

require 'minitest/autorun'

# Demonstrates the way that refinements are applied in Ruby 2.0.0preview1.

module RegularStringCounts
  refine String do
    def num_caps
      self.scan(/[A-Z]/).count
    end
  end
end

module Always42Caps
  refine String do
    def num_caps ; 42 ; end
  end
end

class Person
  attr_reader :name

  using RegularStringCounts

  def initialize(name)
    @name = name
  end

  def caps_in_name
    name.num_caps
  end
end

describe "simple refinements on a class" do
  it "should use the refined method" do
    Person.new("JoeY").caps_in_name.must_equal 2
  end
end

describe "when eval'ing code inside a class that has used refinements" do
  it "should use the refinement" do
    Person.new("JoeY").instance_eval{ "Test STRING".num_caps.must_equal 7 }
  end
end

describe "on an class inherited from one that is refined" do
  class Programmer < Person ; end

  it "should use the refined method from the parent class" do
    Programmer.new("JoeY").caps_in_name.must_equal 2
  end
end

describe "refinements affecting context where method is invoked in class hierarchy" do
  it "should prefer the refinement applied in the parent class where method is invoked" do
    class MoreRefinedPerson < Person
      using Always42Caps
    end

    # Ruby ignores the child class refinement, since the parent class actually responds to
    # the message :caps_in_name. Is this intended behavior or a bug?
    MoreRefinedPerson.new("JoeY").caps_in_name.must_equal 2
  end
end

describe "refinement rules based on the calling context" do
  class Foo ; end # Foo is unrefined

  it "should not respond to the method when it is not defined in the calling context or on the Foo class (sanity check)" do
    Foo.new.instance_eval{ proc {'Hey'.num_caps}.must_raise NoMethodError }
  end

  it "should respond to the method when it is defined in the calling context" do
    using RegularStringCounts

    Foo.new.instance_eval{ 'Hey'.num_caps.must_equal 1 }
  end
end

I hate this so much... :(