Factory Method in Ruby
Factory method is a creational design pattern which solves the problem of creating product objects without specifying their concrete classes.
The Factory Method defines a method, which should be used for creating objects instead of using a direct constructor call (new operator). Subclasses can override this method to change the class of objects that will be created.
If you can’t figure out the difference between various factory patterns and concepts, then read our Factory Comparison.
Complexity:
Popularity:
Usage examples: The Factory Method pattern is widely used in Ruby code. It’s very useful when you need to provide a high level of flexibility for your code.
Identification: Factory methods can be recognized by creation methods that construct objects from concrete classes. While concrete classes are used during the object creation, the return type of the factory methods is usually declared as either an abstract class or an interface.
Conceptual Example
This example illustrates the structure of the Factory Method 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 Creator class declares the factory method that is supposed to return an # object of a Product class. The Creator's subclasses usually provide the # implementation of this method. class Creator # Note that the Creator may also provide some default implementation of the # factory method. def factory_method raise NotImplementedError, "#{self.class} has not implemented method '#{__method__}'" end # Also note that, despite its name, the Creator's primary responsibility is # not creating products. Usually, it contains some core business logic that # relies on Product objects, returned by the factory method. Subclasses can # indirectly change that business logic by overriding the factory method and # returning a different type of product from it. def some_operation # Call the factory method to create a Product object. product = factory_method # Now, use the product. "Creator: The same creator's code has just worked with #{product.operation}" end end # Concrete Creators override the factory method in order to change the resulting # product's type. class ConcreteCreator1 < Creator # Note that the signature of the method still uses the abstract product type, # even though the concrete product is actually returned from the method. This # way the Creator can stay independent of concrete product classes. def factory_method ConcreteProduct1.new end end class ConcreteCreator2 < Creator # @return [ConcreteProduct2] def factory_method ConcreteProduct2.new end end # The Product interface declares the operations that all concrete products must # implement. class Product # return [String] def operation raise NotImplementedError, "#{self.class} has not implemented method '#{__method__}'" end end # Concrete Products provide various implementations of the Product interface. class ConcreteProduct1 < Product # @return [String] def operation '{Result of the ConcreteProduct1}' end end class ConcreteProduct2 < Product # @return [String] def operation '{Result of the ConcreteProduct2}' end end # The client code works with an instance of a concrete creator, albeit through # its base interface. As long as the client keeps working with the creator via # the base interface, you can pass it any creator's subclass. def client_code(creator) print "Client: I'm not aware of the creator's class, but it still works.\n"\ "#{creator.some_operation}" end puts 'App: Launched with the ConcreteCreator1.' client_code(ConcreteCreator1.new) puts "\n\n" puts 'App: Launched with the ConcreteCreator2.' client_code(ConcreteCreator2.new) output.txt: Execution result
App: Launched with the ConcreteCreator1. Client: I'm not aware of the creator's class, but it still works. Creator: The same creator's code has just worked with {Result of the ConcreteProduct1} App: Launched with the ConcreteCreator2. Client: I'm not aware of the creator's class, but it still works. Creator: The same creator's code has just worked with {Result of the ConcreteProduct2} 
