immutable.rb

def Immutable(object)
  Immutable.create(object)
end

class Immutable
  # turns an object, which can be a hash or array of hashes, arrays, and scalars
  # into an object which you can use to access with dot methods. 
  def self.create(object, max_depth = 5)
    case object
    when Array
      raise ArgumentError, 'Object nested too deep (or inner loop?)' if max_depth < 0
      object.map { |obj| create obj, max_depth - 1 }
    when Hash
      Immutable.new(object)
    else
      object
    end
  end

  private

  def initialize(hsh)
    @hsh = hsh
  end

  def method_missing(sym, *args, &block)
    if args.empty? && !block
      begin
        value = @hsh.fetch(sym.to_sym) { @hsh.fetch(sym.to_s) }
        return Immutable.create(value)
      rescue KeyError
        STDERR.puts "Missing attribute #{sym} for Immutable w/#{@hsh.inspect}"
      end
    end

    super
  end

  public

  def respond_to?(sym)
    super || @hsh.key?(sym.to_s) || @hsh.key?(sym.to_sym)
  end

  def ==(other)
    @hsh == other
  end
end

if __FILE__ == $0
  
require "test-unit"

class Immutable::TestCase < Test::Unit::TestCase
  def hsh
    {
      a: "a-value",
      "b": "b-value",
      "child": {
        name: "childname",
        grandchild: {
          name: "grandchildname"
        }
      },
      "children": [
        "anna",
        "arthur",
        {
          action: {
            keep_your_mouth_shut: true
          }
        }
      ]
    }
  end

  def immutable
    Immutable hsh
  end

  def test_hash_access
    assert_equal "a-value", immutable.a
    assert_equal "b-value", immutable.b
  end

  def test_comparison
    immutable = Immutable hsh

    assert_equal immutable, hsh
    assert_not_equal({}, immutable)
  end

  def test_child_access
    child = immutable.child
    assert_kind_of(Immutable, child)
    assert_equal "childname", immutable.child.name
    assert_equal "grandchildname", immutable.child.grandchild.name
  end

  def test_array_access
    assert_kind_of(Array, immutable.children)
    assert_equal 3, immutable.children.length
    assert_equal "anna", immutable.children[0]

    assert_kind_of(Immutable, immutable.children[2])
    assert_equal true, immutable.children[2].action.keep_your_mouth_shut
  end

  def test_base_class
    assert_nothing_raised {  
      immutable.object_id
    }
  end

  def test_missing_keys
    assert_raise(NoMethodError) { 
      immutable.foo
    }
  end

  def test_skip_when_args_or_block
    assert_raise(NoMethodError) {
      immutable.a(1,2,3)
    }
    assert_raise(NoMethodError) {
      immutable.a { :dummy }
    }
  end
end

end