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how-it-works

How PHP-DI works

Do you want to help out improving PHP-DI? Or are you simply curious? Here is a short presentation of how PHP-DI works.

Global architecture

The main component is the Container class. It is created by a ContainerBuilder, which is just a helper class.

It is the entry point from the user's point of view, it is also the component that coordinates all other sub-components.

Its main role is to return entries by their entry name:

$entry = $container->get('entryName');

A container instance has the following sub-components:

  • a DefinitionSource that returns a Definition for an entry name (by looking in several sub-definition sources)
  • a list of DefinitionResolver that take a Definition and resolve it to a value (f.e. if it's an object, it will create it)

Definitions

A definition defines what an entry is:

  • a simple value (string, number, object instance…): ValueDefinition
  • a factory/callable returning the value: FactoryDefinition
  • a definition of an entry alias: Reference
  • a definition of a class: ObjectDefinition
  • a definition of an environment variable: EnvironmentVariableDefinition

The class definition describes how the container should create a class instance (what parameters the constructor takes, …).