Introduction

Dependency Injection

Dependency Injection (here-in called DI) refers to the act of providing dependencies for an object during instantiation or via a method call. A basic example looks like this:

$b = new MovieLister(new MovieFinder());

Above, MovieFinder is a dependency of MovieLister, and MovieFinder was injected into MovieLister.

If you are not familiar with the concept of DI, here are a couple of great reads:

zend-servicemanager

Zend\Di is an example of an Inversion of Control (IoC) container. IoC containers are widely used to create object instances that have all dependencies resolved and injected. Dependency Injection containers are one form of IoC, but not the only form.

Zend Framework ships with another form of IoC as well, zend-servicemanager. Unlike zend-di, zend-servicemanager is code-driven, meaning that you tell it what class to instantiate, or provide a factory for the given class. This approach offers several benefits:

  • Easier to debug (error stacks take you into your factories, not the dependency injection container).
  • Easier to setup (write code to instantiate objects, instead of configuration).
  • Faster (zend-di has known performance issues due to the approaches used).

Unless you have specific needs for a dependency injection container versus more general Inversion of Control, we recommend using zend-servicemanager for the above reasons.

Dependency Injection Containers

When your code is written in such a way that all your dependencies are injected into consuming objects, you might find that the simple act of wiring an object has gotten more complex. When this becomes the case, and you find that this wiring is creating more boilerplate code, this makes for an excellent opportunity to utilize a Dependency Injection Container.

In it's simplest form, a Dependency Injection Container (here-in called a DiC for brevity), is an object that is capable of creating objects on request and managing the "wiring", or the injection of required dependencies, for those requested objects. Since the patterns that developers employ in writing DI capable code vary, DiC's are generally either in the form of smallish objects that suit a very specific pattern, or larger DiC frameworks.

zend-di is a DiC framework. While for the simplest code there is no configuration needed, and the use cases are quite simple, zend-di is capable of being configured to wire these complex use cases