Abstract Factory in Ruby
Abstract Factory is a creational design pattern, which solves the problem of creating entire product families without specifying their concrete classes.
Abstract Factory defines an interface for creating all distinct products but leaves the actual product creation to concrete factory classes. Each factory type corresponds to a certain product variety.
The client code calls the creation methods of a factory object instead of creating products directly with a constructor call (new operator). Since a factory corresponds to a single product variant, all its products will be compatible.
Client code works with factories and products only through their abstract interfaces. This lets the client code work with any product variants, created by the factory object. You just create a new concrete factory class and pass it to the client code.
If you can’t figure out the difference between various factory patterns and concepts, then read our Factory Comparison.
Complexity:
Popularity:
Usage examples: The Abstract Factory pattern is pretty common in Ruby code. Many frameworks and libraries use it to provide a way to extend and customize their standard components.
Identification: The pattern is easy to recognize by methods, which return a factory object. Then, the factory is used for creating specific sub-components.
Conceptual Example
This example illustrates the structure of the Abstract Factory 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 Abstract Factory interface declares a set of methods that return different
# abstract products. These products are called a family and are related by a
# high-level theme or concept. Products of one family are usually able to
# collaborate among themselves. A family of products may have several variants,
# but the products of one variant are incompatible with products of another.
class AbstractFactory
# @abstract
def create_product_a
raise NotImplementedError, "#{self.class} has not implemented method '#{__method__}'"
end
# @abstract
def create_product_b
raise NotImplementedError, "#{self.class} has not implemented method '#{__method__}'"
end
end
# Concrete Factories produce a family of products that belong to a single
# variant. The factory guarantees that resulting products are compatible. Note
# that signatures of the Concrete Factory's methods return an abstract product,
# while inside the method a concrete product is instantiated.
class ConcreteFactory1 < AbstractFactory
def create_product_a
ConcreteProductA1.new
end
def create_product_b
ConcreteProductB1.new
end
end
# Each Concrete Factory has a corresponding product variant.
class ConcreteFactory2 < AbstractFactory
def create_product_a
ConcreteProductA2.new
end
def create_product_b
ConcreteProductB2.new
end
end
# Each distinct product of a product family should have a base interface. All
# variants of the product must implement this interface.
class AbstractProductA
# @abstract
#
# @return [String]
def useful_function_a
raise NotImplementedError, "#{self.class} has not implemented method '#{__method__}'"
end
end
# Concrete Products are created by corresponding Concrete Factories.
class ConcreteProductA1 < AbstractProductA
def useful_function_a
'The result of the product A1.'
end
end
class ConcreteProductA2 < AbstractProductA
def useful_function_a
'The result of the product A2.'
end
end
# Here's the the base interface of another product. All products can interact
# with each other, but proper interaction is possible only between products of
# the same concrete variant.
class AbstractProductB
# Product B is able to do its own thing...
def useful_function_b
raise NotImplementedError, "#{self.class} has not implemented method '#{__method__}'"
end
# ...but it also can collaborate with the ProductA.
#
# The Abstract Factory makes sure that all products it creates are of the same
# variant and thus, compatible.
def another_useful_function_b(_collaborator)
raise NotImplementedError, "#{self.class} has not implemented method '#{__method__}'"
end
end
# Concrete Products are created by corresponding Concrete Factories.
class ConcreteProductB1 < AbstractProductB
# @return [String]
def useful_function_b
'The result of the product B1.'
end
# The variant, Product B1, is only able to work correctly with the variant,
# Product A1. Nevertheless, it accepts any instance of AbstractProductA as an
# argument.
def another_useful_function_b(collaborator)
result = collaborator.useful_function_a
"The result of the B1 collaborating with the (#{result})"
end
end
class ConcreteProductB2 < AbstractProductB
# @return [String]
def useful_function_b
'The result of the product B2.'
end
# The variant, Product B2, is only able to work correctly with the variant,
# Product A2. Nevertheless, it accepts any instance of AbstractProductA as an
# argument.
def another_useful_function_b(collaborator)
result = collaborator.useful_function_a
"The result of the B2 collaborating with the (#{result})"
end
end
# The client code works with factories and products only through abstract types:
# AbstractFactory and AbstractProduct. This lets you pass any factory or product
# subclass to the client code without breaking it.
def client_code(factory)
product_a = factory.create_product_a
product_b = factory.create_product_b
puts product_b.useful_function_b
puts product_b.another_useful_function_b(product_a)
end
# The client code can work with any concrete factory class.
puts 'Client: Testing client code with the first factory type:'
client_code(ConcreteFactory1.new)
puts "\n"
puts 'Client: Testing the same client code with the second factory type:'
client_code(ConcreteFactory2.new)
output.txt: Execution result
Client: Testing client code with the first factory type:
The result of the product B1.
The result of the B1 collaborating with the (The result of the product A1.)
Client: Testing the same client code with the second factory type:
The result of the product B2.
The result of the B2 collaborating with the (The result of the product A2.)
