Prototype in Ruby

Prototype is a creational design pattern that allows cloning objects, even complex ones, without coupling to their specific classes.

All prototype classes should have a common interface that makes it possible to copy objects even if their concrete classes are unknown. Prototype objects can produce full copies since objects of the same class can access each other’s private fields.

Learn more about Prototype

Usage of the pattern in Ruby

Complexity:

Popularity:

Usage examples: The Prototype pattern is available in Ruby out of the box with a Cloneable interface.

Identification: The prototype can be easily recognized by a clone or copy methods, etc.

Conceptual Example

This example illustrates the structure of the Prototype design pattern. It focuses on answering these questions:

What classes does it consist of?
What roles do these classes play?
In what way the elements of the pattern are related?

main.rb: Conceptual example

# The example class that has cloning ability. We'll see how the values of field
# with different types will be cloned.
class Prototype
  attr_accessor :primitive, :component, :circular_reference

  def initialize
    @primitive = nil
    @component = nil
    @circular_reference = nil
  end

  # @return [Prototype]
  def clone
    @component = deep_copy(@component)

    # Cloning an object that has a nested object with backreference requires
    # special treatment. After the cloning is completed, the nested object
    # should point to the cloned object, instead of the original object.
    @circular_reference = deep_copy(@circular_reference)
    @circular_reference.prototype = self
    deep_copy(self)
  end

  # deep_copy is the usual Marshalling hack to make a deep copy. But it's rather
  # slow and inefficient, therefore, in real applications, use a special gem
  private def deep_copy(object)
    Marshal.load(Marshal.dump(object))
  end
end

class ComponentWithBackReference
  attr_accessor :prototype

  # @param [Prototype] prototype
  def initialize(prototype)
    @prototype = prototype
  end
end

# The client code.
p1 = Prototype.new
p1.primitive = 245
p1.component = Time.now
p1.circular_reference = ComponentWithBackReference.new(p1)

p2 = p1.clone

if p1.primitive == p2.primitive
  puts 'Primitive field values have been carried over to a clone. Yay!'
else
  puts 'Primitive field values have not been copied. Booo!'
end

if p1.component.equal?(p2.component)
  puts 'Simple component has not been cloned. Booo!'
else
  puts 'Simple component has been cloned. Yay!'
end

if p1.circular_reference.equal?(p2.circular_reference)
  puts 'Component with back reference has not been cloned. Booo!'
else
  puts 'Component with back reference has been cloned. Yay!'
end

if p1.circular_reference.prototype.equal?(p2.circular_reference.prototype)
  print 'Component with back reference is linked to original object. Booo!'
else
  print 'Component with back reference is linked to the clone. Yay!'
end

output.txt: Execution result

Primitive field values have been carried over to a clone. Yay!
Simple component has been cloned. Yay!
Component with back reference has been cloned. Yay!
Component with back reference is linked to the clone. Yay!