The package provides syntax constructs describing a way to create and configure a service or an object. It is used by yiisoft/di and yiisoft/factory but could be used in other PSR-11 compatible packages as well.

The following are provided:

• Definitions describing services or objects to create. This includes syntax, its validation and resolving it to objects.
• References and dynamic references to point to other definitions. These include additional utility to refer to multiple definitions at once.

• PHP 8.0 or higher.

The package could be installed with composer:

composer require yiisoft/definitions

Definition is describing a way to create and configure a service, an object or return any other value. It must implement Yiisoft\Definitions\Contract\DefinitionInterface that has a single method resolve(ContainerInterface $container). References are typically stored in the container or a factory and are resolved into object at the moment of obtaining a service instance or creating an object.

Array definition allows describing a service or an object declaratively:

use \Yiisoft\Definitions\ArrayDefinition;

$definition = ArrayDefinition::fromConfig([
    'class' => MyServiceInterface::class,
    '__construct()' => [42], 
    '$propertyName' => 'value',
    'setName()' => ['Alex'],
]);
$object = $definition->resolve($container);

In the above:

• class contains the name of the class to be instantiated.
• __construct() holds an array of constructor arguments.
• The rest of the config are property values (prefixed with $) and method calls, postfixed with (). They are set/called in the order they appear in the array.

For multiple method call postfix key with unique string, for example:

[
    'class' => Collector::class,
    'add()' => ['Alex'],
    'add()2' => ['Mike'],
]

Callable definition builds an object by executing a callable injecting dependencies based on types used in its signature:

use \Yiisoft\Definitions\CallableDefinition;

$definition = new CallableDefinition(
    fn (SomeFactory $factory) => $factory->create('args')
);
$object = $definition->resolve($container);

// or 

$definition = new CallableDefinition(
    fn () => MyFactory::create('args')
);
$object = $definition->resolve($container);

// or

$definition = new CallableDefinition(
    [MyFactory::class, 'create']
);
$object = $definition->resolve($container);

In the above we use a closure, a static call and a static method passed as array-callable. In each case we determine and pass dependencies based on the types of arguments in the callable signature.

Parameter definition resolves an object based on information from ReflectionParameter instance:

use \Yiisoft\Definitions\ParameterDefinition;

$definition = new ParameterDefinition($reflectionParameter);
$object = $definition->resolve($container);

It is mostly used internally when working with callables.

Value definition resolves value passed as is:

use \Yiisoft\Definitions\ValueDefinition;

$definition = new ValueDefinition(42, 'int');
$value = $definition->resolve($container); // 42

References point to other definitions so when defining a definition you can use other definitions as its dependencies:

[
    InterfaceA::class => ConcreteA::class,
    'alternativeForA' => ConcreteB::class,
    MyService::class => [
        '__construct()' => [
            Reference::to('alternativeForA'),
        ],
    ],
]

Optional reference returns null when there's no corresponding definition in container:

[
    MyService::class => [
        '__construct()' => [
            // If container doesn't have definition for `EventDispatcherInterface` reference returns `null`
            // when resolving dependencies
            Reference::optional(EventDispatcherInterface::class), 
        ],
    ],
]

The DynamicReference defines a dependency to a service not defined in the container:

[
   MyService::class => [
       '__construct()' => [
           DynamicReference::to([
               'class' => SomeClass::class,
               '$someProp' => 15
           ])
       ]
   ]
]

In order to pass an array of IDs as references to a property or an argument, Yiisoft\Definitions\ReferencesArray or Yiisoft\Definitions\DynamicReferencesArray could be used:

//params.php
return [
   'yiisoft/data-response' => [
       'contentFormatters' => [
           'text/html' => HtmlDataResponseFormatter::class,
           'application/xml' => XmlDataResponseFormatter::class,
           'application/json' => JsonDataResponseFormatter::class,
       ],
   ],
];

//web.php

ContentNegotiator::class => [
    '__construct()' => [
        'contentFormatters' => ReferencesArray::from($params['yiisoft/data-response']['contentFormatters']),
    ],
],

Definition storage could be used to hold and obtain definitions and check if a certain definition could be instantiated. Usually it is used by an implementation using the definitions:

use Yiisoft\Definitions\DefinitionStorage;

$storage = new DefinitionStorage([
    MyInterface::class => MyClass::class,
]);
$storage->setDelegateContainer($fallbackContainer);

if (!$storage->has(MyInterface::class)) {
    $buildStack = $storage->getBuildStack();
    // ...
}

In the above $buildStack will contain a stack with definition IDs in the order the latest dependency obtained would be built.

By default, if a class is checked in has() and it is not explicitly defined, the storage tries to autoload it first before failing. The storage may also work in a strict mode when everything in it should be defined explicitly:

use Yiisoft\Definitions\DefinitionStorage;

$storage = new DefinitionStorage([], true);
var_dump($storage->has(EngineMarkOne::class));

has() will return false even if EngineMarkOne exists.

• Internals

If you need help or have a question, the Yii Forum is a good place for that. You may also check out other Yii Community Resources.

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