Code generation

Overview of code generation

The Magento application generates code to create non-existent classes. As an example, look at the \Magento\Customer\Model\Resource\AddressRepository constructor. A snippet follows:

...
    public function __construct(
        \Magento\Customer\Model\AddressFactory $addressFactory,
...

The first constructor parameter has a type of Magento\Customer\Model\AddressFactory. However, this class does not exist in \Magento\Customer\Model in the Magento 2 codebase. The Magento application generates this class because its name uses a recognized convention (in this case, because the name ends with Factory).

Unlike some other languages or libraries, you can look at the generated code on the file system to see what really happens and still debug the code.

When is code generated?

Provided the Magento application is not set for production mode, code is generated when the Magento application cannot find a class when executing code.

In particular,

• A Factory class creates instances of a type. See Instantiating objects with factories for more information. Factories are directly referenced within application code.

• You can designate a Proxy to be generated for a type in order to ensure the type is not instantiated until it is needed. See Proxies for more information. Proxies are directly referenced within DI configuration.

• Interceptor classes are automatically generated to facilitate Magento’s plugin system. An interceptor class extends a type and is returned by the Object Manager to allow multiple plugin classes to inject logic into different methods. Interceptors work behind the scenes and are not directly referenced in application code.

You can also use the code compiler to generate code at any time. In Magento 2, “compiling” your application means performing code generation for any eligible class encountered by the configuration/code scanner, as well as performing a number of different dependency injection optimizations.

Why should you regenerate code?

Suppose a Factory or Proxy class for a Customer class is generated and the Customer class has new methods added to it. Because a Factory or Proxy exists on the file system, it is not regenerated. However, the Factory or Proxy implementation is now incomplete because it does not have the new methods. In this case, you must regenerate the Factory or Proxy class.

If the code generator implementation itself is changed, you must regenerate all the classes. This is rare, however.

Advantages of generating code

Code generation is required in Magento 2. Generating code assures you of the following:

• The code is correct. You don’t have to worry that the generated code is delegating to the wrong method or forgetting a semicolon, and you don’t have to write tests for the generated code.
• Code generation writes the boilerplate code to enable you to write more challenging and interesting code.

• Consistent implementation.

  All generated Factories work the same way. After you know how one Factory works, you know how they all work.

Object Manager responsibility for code compilation

When code changes as discussed in the preceding section, the Object Manager compiles it.

The code compiler creates generated/metadata/global.php, which is a PHP serialized map of all constructor definitions mixed with object linking configuration defined in di.xml. di.xml is the dependency injection configuration. There is a global app/etc/di.xml and there can one defined for every module.