Ruby Fundamental - Diferenças de "include" e "extend" na inclusão de módulos

modulos_include_extend_01.rb

module Numbers
  def one
    puts "1"
  end

  def two
    puts "2"
  end
end

module Ordinals
  def first
    puts "1st"
  end

  def second
    puts "2nd"
  end
end

modulos_include_extend_02.rb

class MyClass1
  include Numbers
  extend Ordinals
end

modulos_include_extend_03.rb

m1 = MyClass1.new
m1.one # => "1"
m1.two # => "2"
m1.first # => NoMethodError: undefined method `first' for #<MyClass1:0x035930>
m1.second # => NoMethodError: undefined method `second' for #<MyClass1:0x035930>

MyClass1.one # => NoMethodError: undefined method `one' for MyClass1:Class
MyClass1.two # => NoMethodError: undefined method `two' for MyClass1:Class
MyClass1.first # => "1st"
MyClass1.second # => "2nd"

modulos_include_extend_04.rb

class MyClass2
end

MyClass2.extend Ordinals

MyClass2.first # => "1st"
MyClass2.second # => "2nd"

m2 = MyClass2.new
m2.first # => NoMethodError: undefined method `first' for #<MyClass2:0x10402a8>
m2.second # => NoMethodError: undefined method `second' for #<MyClass2:0x10402a8>

modulos_include_extend_05.rb

MyClass2.include Ordinals # => NoMethodError: private method `include' called for MyClass2:Class

modulos_include_extend_06.rb

class MyClass3
end

m3 = MyClass3.new
m3.extend Ordinals

m3.first # => "1st"
m3.second # => "2nd"

MyClass3.first # => NoMethodError: undefined method `first' for MyClass3:Class
MyClass3.second # => NoMethodError: undefined method `second' for MyClass3:Class

MyClass3.new.first # => NoMethodError: undefined method `first' for #<MyClass3:0x1055f04>
MyClass3.new.second # => NoMethodError: undefined method `second' for #<MyClass3:0x105bf30>

modulos_include_extend_07.rb

class MyClass4
end

MyClass4.send(:include, Numbers)

m4 = MyClass4.new
m4.one # => "1"
m4.two # => "2"

MyClass4.one # => NoMethodError: undefined method `one' for MyClass4:Class
MyClass4.two # => NoMethodError: undefined method `two' for MyClass4:Class

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