Ruby/Class/clone

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                                      # => "spring"
s3.string                                      # => "spring"

material = "cotton"
class << material
  def definition
     puts "this is a test."
  end
end
puts material.definition
"cotton".definition
# NoMethodError: undefined method "definition" for "cotton":String
material.clone.definition
 
material.dup.definition
# NoMethodError: undefined method "definition" for "cotton":String

s1 = "foo"                                       # => "foo"
s2 = s1.clone                                    # => "foo"
s1[0] = "b"
[s1, s2]                                         # => ["boo", "foo"]