s1 = 'foo'

s2 = s1.clone

s1[0] = 'b'
[s1, s2]

material = 'cotton'
class << material
  def definition
     puts 'The better half of velour.'
  end
end
material.definition

The better half of velour.

The better half of velour.

'cotton'.definition

NoMethodError: undefined method `definition' for "cotton":String
...

NoMethodError: undefined method `definition' for "cotton":String
	from (irb):12

material.clone.definition

The better half of velour.

The better half of velour.

material.dup.definition               

NoMethodError: undefined method `definition' for "cotton":String
...

NoMethodError: undefined method `definition' for "cotton":String
	from (irb):14

class StringHolder 
  attr_reader :string
  def initialize(string)
    @string = string
  end
end
s1 = StringHolder.new('string')
s2 = s1.dup
s3 = s1.clone
s1.string[1] = 'p'
s2.string

s3.string

class Object
  def deep_copy
    Marshal.load(Marshal.dump(self))
  end
end
s1 = StringHolder.new('string')
s2 = s1.deep_copy
s1.string[1] = 'p'
s1.string

s2.string

class << s1
  def definition
     puts "We hold strings so you don't have to."
  end  
end
s1.deep_copy

TypeError: singleton can't be dumped
...

TypeError: singleton can't be dumped
	from (irb):29:in `dump'
	from (irb):29:in `deep_copy'
	from (irb):42

class StringHolder
  def initialize_copy(from)
   @string = from.string.dup
  end
end
s1 = StringHolder.new('string')
s2 = s1.dup
s3 = s1.clone
s1.string[1] = "p"
s2.string

s3.string