AbstractClass

example 
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class AbstractKlass
  def method_name
    puts "#{hello} #{name}"
  end
end

class ConcreteKlass < AbstractKlass
  def hello; "Hello"; end
  def name; "Rubyist"; end

  # def hello
  #   "Hello"
  # end

  # def name
  #   "Rubyist"
  # end
end

ConcreteKlass.new.method_name # => "Hello Rubyist"