undef keyword with symbol

I see something like this:

require "ostruct" class OptionsWrapper < OpenStruct   undef :id, :class

  def (key)     send(key)   end

  def =(key, value)     send("#{key}=", value)   end

  def method_missing(method, *args, &block)     return @table.include?(method) ? @table.send(method) : nil if %w(id class).include?(method.to_s)

    @table.respond_to?(method) ? @table.send(method, *args, &block) : super   end end

I know OpenStruct is a class part of standard ruby library allowing you to arbitrarily create methods on an object instance. I know that undef allows you to set a method to nil. But I dont see why it is needed in this case.

thanks for response

id and class are built-in ruby methods that are present on all object instances.

Rails uses them in a different manner than the default Ruby implementation.

They are undefined so that they can be picked up by the method_missing method.

that makes sense, thanks