testing.rb

class DoNotDump < Module
  class << self
    alias [] new
  end

  def initialize *ignored_ivars
    @ignored = -> ivar { ignored_ivars.include? ivar }
  end

  def included base
    base.class_exec @ignored do |ignored|
      @@ignored = ignored

      def marshal_load data
        Marshal.load(data).each { |ivar, value| instance_variable_set ivar, value }
      end

      def marshal_dump
        data = instance_variables.grep_v(@@ignored).map do |ivar|
          [ivar, instance_variable_get(ivar)]
        end

        Marshal.dump data
      end
    end
  end
end

class Example
  def initialize
    @unserializable = ->{}
  end
end

class Example
  include DoNotDump[:@unserializable]
end

p Marshal.load Marshal.dump Example.new