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PHP-DI is a Container that makes Dependency Injection as practical as possible.

PHP-DI also tries to avoid falling into the trap of the "Service Locator" antipattern and help you do real dependency injection.

Features

• Simple to start with
• Supports different configuration alternatives to suit every taste:
  • Reflection: zero configuration, intelligent guessing
  • Annotations: modern, practical and simple
  • PHP code: if you like complete control and auto-completion
  • PHP array: allows you to store it in a configuration file
  • YAML: elegant and concise
  • XML (work in progress): more verbose, but more classic
• Performances: supports a large number of Caches
• Offers lazy injection: lazy-loading of dependencies (WIP)
• Supports constructor injection, setter injection and property injection

Usage

Let's go to the Getting started guide!

And there is a complete documentation waiting for you.

What is dependency injection, and why use PHP-DI

You can first read the introduction to dependency injection with an example.

Dependency injection and DI containers are separate notions, and one should use of a container only if it makes things more practical (which is not always the case depending on the container you use).

PHP-DI is about this: make dependency injection more practical.

How classic PHP code works

Here is how a code not using DI will roughly work:

• Application needs Foo (e.g. a controller), so:
• Application creates Foo
• Application calls Foo
  • Foo needs Bar (e.g. a service), so:
  • Foo creates Bar
  • Foo calls Bar
    • Bar needs Bim (a service, a repository, …), so:
    • Bar creates Bim
    • Bar does something

How Dependency Injection works

Here is how a code using DI will roughly work:

• Application needs Foo, which needs Bar, which needs Bim, so:
• Application creates Bim
• Application creates Bar and gives it Bim
• Application creates Foo and gives it Bar
• Application calls Foo
  • Foo calls Bar
    • Bar does something

This is the pattern of Inversion of Control. The control of the dependencies is inversed from one being called to the one calling.

The main advantage: the one at the end of the caller chain is always you. So you can control every dependencies: you have a complete control on how your application works. You can replace a dependency by another (one you made for example).

For example that wouldn't be so easy if Library X uses Logger Y and you have to change the code of Library X to make it use your logger Z.

How code using PHP-DI works

Now how does a code using PHP-DI works:

• Application needs Foo so:
• Application gets Foo from the Container, so:
  • Container creates Bim
  • Container creates Bar and gives it Bim
  • Container creates Foo and gives it Bar
• Application calls Foo
  • Foo calls Bar
    • Bar does something

In short, PHP-DI takes away all the work of creating and injecting dependencies.