output

[]
HELLO
hello
[{:upcase!=>"hello"}, {:downcase!=>"HELLO"}]
[Finished in 0.1s]

string_story.rb

class StringWithLogs < String
  attr_reader :story

  def enable_story
    @story = []
      class << self
        self.instance_methods.reject{|x| !x.to_s.include?('!')}.each do |m|
          alias_method "old_#{m}".to_sym, m
          define_method(m){|*args|@story << {m => dup} ;super(*args)}
        end
      end
  end
end

p = StringWithLogs.new('hello')

p.enable_story

p p.story
puts p.upcase!
puts p.downcase!
p p.story

Debugging masta!