What is the difference between the Object methods clone and dup?

[geekelo]

In Ruby, both clone and dup are methods used to create a shallow copy of an object. However, there are some differences between the two:

1. Handling of Frozen Objects:

   • clone will produce a copy of the object, including its frozen state. If the original object is frozen, the cloned object will also be frozen.
   • dup does not copy the frozen state. The duplicated object will not be frozen even if the original was.

2. Handling of Tainted Objects:

   • clone copies the tainted state of the original object. If the original is tainted, the clone will also be tainted.
   • dup does not copy the tainted state. The duplicated object will not be tainted even if the original was.

3. Initialization of Instance Variables:

   • Both clone and dup copy the instance variables of the original object to the new object. However, they do not call the initialize method on the new object.

4. Module Inclusion:

   • clone preserves the singleton class and any modules that are included in the singleton class of the original object.
   • dup does not copy the singleton class or any included modules.

Here's an example to illustrate the differences:

module MyModule
  def my_method
    puts "Hello from MyModule!"
  end
end

class MyClass
  include MyModule
end

obj = MyClass.new
obj_clone = obj.clone
obj_dup = obj.dup

puts obj_clone.my_method # Outputs: Hello from MyModule!
puts obj_dup.my_method   # Raises NoMethodError

puts obj_clone.frozen?   # Outputs: true
puts obj_dup.frozen?     # Outputs: false

puts obj_clone.tainted?  # Outputs: true
puts obj_dup.tainted?    # Outputs: false

In this example, clone preserves the module inclusion and the frozen and tainted states, while dup does not. Choose the method that fits your specific use case and the behavior you desire.