The package provides definition syntax

3.3.0 2024-03-16 13:31 UTC



Yii Definitions

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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

General usage


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()' => [

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

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

   MyService::class => [
       '__construct()' => [
               '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:

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


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

Definition storage

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,

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);

has() will return false even if EngineMarkOne exists.


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.


The Yii Definitions is free software. It is released under the terms of the BSD License. Please see LICENSE for more information.

Maintained by Yii Software.

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