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singleton_class_eval

🏗️ Modify Singletons with singleton_class_eval​

To extend or override behavior on a single object instance, use singleton_class with class_eval. This avoids global monkey-patches and keeps modifications confined to one object.

str = "hello"
str.singleton_class.class_eval do
  def excited
    self.upcase + "!!!"
  end
end

puts str.excited  # => "HELLO!!!"
puts "world".respond_to?(:excited)  # => false