Spike: Extensible Deep Freeze

ice_nine.rb

# I didn't want to monkey patch #deep_freeze into core classes, plus I wanted
# to have a way to easily add new classes without modifying a case statement or
# similar. Plus I wanted a way for people to be able to specify exceptions for
# their own classes without patching mine.

module IceNine
  def self.deep_freeze(object)
    return object if object.frozen?
    f = Freezer[object.class.name]
    f.deep_freeze(object)
  end

  class Freezer
    def self.[](name)
      mod, const = name.to_s.split('::', 2)
      const_args = RUBY_VERSION > '1.9' ? [mod, false] : mod
      mod && const_defined?(*const_args) ? const_get(*const_args)[const] : self
    end

    def self.deep_freeze(object)
      object.instance_variables do |ivar|
        IceNine.deep_freeze(object.instance_variable_get(ivar))
      end
      object.freeze
    end

    class Array < self
      def self.deep_freeze(object)
        super object.each { |entry| IceNine.deep_freeze(entry) }
      end
    end

    class Hash < self
      def self.deep_freeze(object)
        super object.each { |key, value|
          IceNine.deep_freeze(key)
          IceNine.deep_freeze(value)
        }
      end
    end

    class Singleton < self
      def self.deep_freeze(object)
        object
      end
    end

    class Numeric < Singleton; end
    class TrueClass < Singleton; end
    class FalseClass < Singleton; end
    class NilClass < Singleton; end
    class Symbol < Singleton; end
  end
end

hash = IceNine.deep_freeze('a' => '1')
puts "Hash is frozen:            #{hash.frozen?}"
puts "Hash Keys are frozen:      #{hash.keys.all?(&:frozen?)}"
puts "Hash Values are frozen:    #{hash.values.all?(&:frozen?)}"

array = IceNine.deep_freeze([ 'a', 'b', 'c' ])
puts "Array is frozen:           #{array.frozen?}"
puts "Array Elements are frozen: #{array.all?(&:frozen?)}"

object = IceNine.deep_freeze(Object.new)
puts "Object is frozen:          #{object.frozen?}"

symbol = IceNine.deep_freeze(:symbol)
puts "Symbol is frozen:          #{symbol.frozen?} (should be false)"

@dkubb I saw your gist but couldn't get it to work on 1.9 – #const_defined? and #const_get have a different method signature. By default (without the second argument set to false) will also search ancestors for the given constant. I updated the gist to reflect this behaviour change.

@myabc I updated the original gist with something I think that will work on 1.9. Its a similar technique to something I did in virtus to work around the api differences, without introducing a separate code path to get similar behaviour.

@myabc oh heh, I see you did the same thing here. Sorry, it's early :) I believe atm rbx needs the same work-around but I need to test against rbx-head, which I'm installing now.

Hmm, looks like rbx has some ivars in each object that I need to exclude from freezing to avoid modifying internal state.