hash_dup.rb

my_dict = { foo: 1, bar: 'baz' }

my_clone = my_dict.dup                  #=> making a shallow copy

my_clone.object_id == my_dict.object_id #=> false, these are different objects
my_clone == my_dict                     #=> true, they contain the same values

my_clone[:qux] = 'wibble'               #=> adding a pair to the clone
my_clone.has_key? :qux                  #=> true, the key was added
my_dict.has_key? :qux                   #=> false, the key was never added to this object, neither was its value

my_clone[:bar].object_id == my_dict[:bar].object_id #=> true, because they reference the same string object

my_clone[:bar].gsub! 'z', 'ss'          #=> mutating the string
my_dict[:bar]                           #=> 'bass', the string has been altered since they both reference the same object

my_clone[:foo] = 2                      #=> changing a reference
my_clone[:foo]                          #=> 2, the reference now points to 2
my_dict[:foo]                           #=> 1, the reference remains where it was originally, since it was never changed


# documentation for dup: http://apidock.com/ruby/Object/dup