how to override methods on class composed in another class or module?

Hey y'all,

I'm using Rails module ActiveModel, which adds useful validation
behavior to descendants, including  by reference to another class,
Errors, that in part composes it.

The initializer for the Errors class is...

   def initialize(base)
      @base     = base
      @messages = ActiveSupport::OrderedHash.new
    end

...and ActiveModel implentations expose an instance of Errors with a
method #errors.

I would like to override particular methods on the Errors instance in my
ActiveModel implementation, sort of like as follows

def errors
   some_state_i_want_to_add_to_the_pseudo_method_overwrite = ...
   super.tap {|e| e.extend
ExtraErrorsBehaviorWithStateFromCallingClassButHowToDoThis }
end

Moreover, I want this errors override to be useful if I inherit from the
ActiveModel implementation. So, in a descendant of the AR implementation
above, I might like to do this...

def errors
   some_additional_state_i_want_to_add_to_the_pseudo_method_overwrite =
...
   super.tap {|e| e.extend
EvenMoreExtraErrorsBehaviorWithStateFromCallingClassButHowToDoThis }
end

Any suggestions?

Thanks,

Grar

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