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class_eval_usage

💡 Add Methods to a Class with class_eval​

class_eval (or module_eval) executes a string or block in the context of a class/module definition. This is useful to inject methods or constants after a class is defined, enabling flexible extensions or plugins.

class Person; end

Person.class_eval do
  def greet
    "Hello from #{self.class}!"
  end
end

p = Person.new
puts p.greet    # => "Hello from Person!"