Under Construction This proposal is under construction and is not ready for review.

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Zend Framework: Zend_DI Component Proposal

Table of Contents

1. Overview

Zend_DI is a dependency injector component, similar in concept to PicoContainer, but smaller and easier to use. The architecture of the Zend_DI component is based on the following concepts:

• Dependency injection is a technique that consists of passing objects via the constructor or setter methods.
• The Container provides an easy way of re-configuring a package to use custom implementations of components.
• Responsibility for object management is taken over by whatever container is being used to manage those objects.

2. References

• Martin Fowler Dependency Injection pattern
• PicoContainer

3. Component Requirements, Constraints, and Acceptance Criteria

• This component will use Reflection.

4. Dependencies on Other Framework Components

• Zend_Config
• Zend_Exception
• Zend_Registry

5. Theory of Operation

Zend_DI minimizes coupling between groups of classes, makes unit testing much simpler, and provides an easy way to re-configure a package to use custom implementations of components. For example:

Once we separate configuration from use, we can easily test the Car with different engines. It's just a matter of re-configuring the package and injecting Zend_Car_Parts_Engine_Gas instead of Zend_Car_Parts_Engine_Fuel.

Zend_DI provides generic factory classes that instantiate instances of classes. These instances are then configured by the container, allowing construction logic to be reused on a broader level. Typically, responsibility for object management is taken over by whatever container is being used to manage those objects.

6. Milestones / Tasks

• Milestone 1: [DONE] Design interface
• Milestone 2: [IN PROGRESS] Write proposal
• Milestone 3: Gather feedback and revise design as necessary
• Milestone 4: Develop full implementation and unit tests
• Milestone 5: Documentation
• Milestone 6: Future enhancements

7. Class Index

• Zend_DI_Container
• Zend_DI_Exception
• Zend_DI_Container_Manager
• Zend_DI_Container_Exception
• Zend_DI_Component_Factory
• Zend_DI_Component_Exception

8. Use Cases

For all of these use cases, I'll use the following classes:

The component handles injections via the constructor or setters methods. In addition, Zend_DI allows the user to map out specifications for components and their dependencies in a configuration file and generate the objects based on that specification. The configuration object can be set using the setConfig() method.

Constructor dependency injection

The configuration array is typically set up in a different class. For example, each package can have its own configuration class (this class can extend Zend_Config), or an XML file. The configuration file holds the components specifications and package dependencies.

Users can map out specifications for components and their dependencies:

Setter dependency injection

Containers

You can tell Zend_DI what classes to manage by adding them to a container (the order of registration has no significance):

Containers can be retrieved using the Zend_DI_Container_Manager::getContainer() method, which returns an instance of the Zend_Registry class.

9. Class Skeletons

• Zend_DI_Container

• Zend_DI_Component_Factory