When To Use Factories vs Abstract Factories

Starting with version 3, Zend\ServiceManager\Factory\AbstractFactoryInterface extends Zend\ServiceManager\Factory\FactoryInterface, meaning they may be used as either an abstract factory, or mapped to a specific service name as its factory.

As an example:

return [
    'factories' => [
        SomeService::class => AnAbstractFactory::class,
    ],
];

Why would you choose one approach over the other?

Comparisons

Approach Pros Cons
Abstract factory One-time setup Performance; discovery of code responsible for creating instance
Factory Performance; explicit mapping to factory responsible Additional (duplicate) setup

Essentially, it comes down to convenience versus explicitness and/or performance.

Convenience

Writing a factory per service is time consuming, and, particularly in early stages of an application, can distract from the actual business of writing the classes and implementations; in addition, since requirements are often changing regularly, this boiler-plate code can be a nuisance.

In such situations, one or more abstract factories — such as the ConfigAbstractFactory, the ReflectionBasedAbstractFactory, or the zend-mvc LazyControllerAbstractFactory — that can handle the bulk of your needs are often worthwhile, saving you time and effort as you code.

Explicitness

The drawback of abstract factories is that lookups by the service manager take longer, and increase based on the number of abstract factories in the system. The service manager is optimized to locate factories, as it can do an immediate hash table lookup; abstract factories involve:

  • Looping through each abstract factory
    • invoking its method for service location
    • if the service is located, using the factory

This means, internally:

  • a hash table lookup (for the abstract factory)
  • invocation of 1:N methods for discovery
    • which may contain additional lookups and/or retrievals in the container
  • invocation of a factory method (assuming succesful lookup)

As such, having an explicit map can aid performance dramatically.

Additionally, having an explicit map can aid in understanding what class is responsible for initializing a given service. Without an explicit map, you need to identify all possible abstract factories, and determine which one is capable of handling the specific service; in some cases, multiple factories might be able to, which means you additionally need to know the order in which they will be queried.

The primary drawback is that you also end up with potentially duplicate information in your configuration:

  • Multiple services mapped to the same factory.
  • In cases such as the ConfigAbstractFactory, additional configuration detailing how to create the service.

Tradeoffs

What it comes down to is which development aspects your organization or project favor. Hopefully the above arguments detail what tradeoffs occur, so you may make an appropriate choice.

Tooling

Starting with 3.2.0, we began offering a variety of console tools to assist you in generating both dependency configuration and factories. Use these to help your code evolve. An expected workflow in your application development evolution is:

  • Usage of the ReflectionBasedAbstractFactory as a "catch-all", so that you do not need to do any factory/dependency configuration immediately.
  • Usage of the ConfigAbstractFactory, mapped to services, once dependencies have settled, to disambiguate dependencies, or to list custom services returning scalar or array values.
  • Finally, usage of the generate-factory-for-class vendor binary to generate actual factory classes for your production-ready code, providing the best performance.

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