test.rb

class FooStruct
  def initialize(attrs)
    # Create a Singleton Class (Anonymous Class) inheriting from FooStruct
    klass = ( class << self; self; end )
    # Loop through the attributes
    attrs.each do |attr|
      # Within the context of the anonymous class...
      klass.class_eval do
        # Define accessors for each of the attributes
        attr_accessor attr.to_sym
      end
    end
  end
end