Test whether a Ruby VM has the hooks we need to implement label propagation for Police.

ll_test.rb

class LabeledString < String
  def +(other)
    LabeledString.new original_plus(other)
  end
end

class String
  alias_method :original_plus, :+

  def +(other)
    if other.instance_of? LabeledString
      LabeledString.new original_plus(other.to_s)
    else
      original_plus other
    end
  end
end

class Regexp
  alias_method :original_match, :match

  def match(string, pos=0)
    if string.instance_of? LabeledString
      if pos == 0
        match_data = original_match string
      else
        match_data = original_match string, pos
      end
      if match_data.nil?
        match_data
      else
        WrappedMatchData.new match_data
      end
    else
      if pos == 0
        original_match string
      else
        original_match string, pos
      end
    end
  end
end

class WrappedMatchData
  def initialize(match_data)
    @match_data = match_data
  end

  def [](index)
    string = @match_data[index]
    if string.nil?
      string
    else
      LabeledString.new string
    end
  end
end

s1 = LabeledString.new "Sekret Name"
s2 = "Public Name"

# Preface output with the VM name.
p RUBY_DESCRIPTION

# This works.
p [(s1 + s2).class, LabeledString]
p [(s2 + s1).class, LabeledString]
p [(s1 + s1).class, LabeledString]
p [(s2 + s2).class, String]

# This needs string interpolation changes to work.
p ["Hi #{s1}".class, LabeledString]
p ["Hi #{s2}".class, String]

# This works.
p [/(name)/i.match(s1)[1].class, LabeledString]
p [/(name)/i.match(s2)[1].class, String]

# This works, but I'm not sure it should.
/(name)/i =~ s1
p [$1.class, LabeledString]
p [$~[1].class, LabeledString]
/(name)/i =~ s2
p [$1.class, String]
p [$~[1].class, String]