Difference between include and extend in Ruby on Rails

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  • include : mixes in specified module methods as instance methods in the target class
  • extend : mixes in specified module methods as class methods in the target class

So is the major difference just this or is a bigger dragon lurking? e.g.

  module ReusableModule
    def module_method
      puts "Module Method: Hi there!"
    end
  end
  
class ClassThatIncludes
    include ReusableModule
  end
  class ClassThatExtends
    extend ReusableModule
  end
  
puts "Include"
  ClassThatIncludes.new.module_method       # "Module Method: Hi there!"
  puts "Extend"
  ClassThatExtends.module_method              # "Module Method: Hi there!"

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