frozen_string = 'Brrrr!'
frozen_string.freeze
frozen_string.gsub('r', 'a')

frozen_string.gsub!('r', 'a')

TypeError: can't modify frozen string
...

TypeError: can't modify frozen string
	from (irb):4:in `gsub!'
	from (irb):4

sequences = [[1,2,3], [1,2,4], [1,4,9]].freeze
sequences << [2,3,5]

TypeError: can't modify frozen array
...

TypeError: can't modify frozen array
	from (irb):6:in `<<'
	from (irb):6

sequences[2] << 16

frozen_string.clone.frozen?

frozen_string.dup.frozen?

frozen_string = 'A new string.'
frozen_string.frozen?

API_KEY = "100f7vo4gg".freeze
API_KEY[0] = 4

TypeError: can't modify frozen string
...

TypeError: can't modify frozen string
	from (irb):13:in `[]='
	from (irb):13

API_KEY = "400f7vo4gg"

warning: already initialized constant API_KEY

class MyClass
  def my_method
    puts "This is the only method allowed in MyClass."
  end
  MyClass.freeze
end
class MyClass
  def my_method
    "I like this implementation of my_method better."
  end
end

TypeError: can't modify frozen class
...

TypeError: can't modify frozen class
	from (irb):22

class MyClass
  def my_other_method
    "Oops, I forgot to implement this method."
  end
end

TypeError: can't modify frozen class
...

TypeError: can't modify frozen class
	from (irb):27

class MySubclass < MyClass
  def my_method
    "This is only one of the methods available in MySubclass."
  end
  def my_other_method
    "This is the other one."
  end
end
MySubclass.new.my_method