~immutable structs

immutable_struct.rb

module ImmutableStruct
  module PropSetter
    attr_reader :props

    def use_struct_props(*props)
      attr_reader *props
      @props = props
    end
  end

  def self.build(*fields)
    Class.new do
      extend PropSetter

      use_struct_props *fields

      def initialize(values)
        self.class.props.each do |field|
          instance_variable_set("@#{field}", values.fetch(field))
        end
      end
    end
  end
end