Dependency Injection Library for PHP

The PHP Dependency Injection library provides a customizable dependency injection framework for projects running on PHP 8.1 or later.

$container = new Suhock\DependencyInjection\Container();
$container->addSingletonClass(MyApplication::class)
    // Add the rest of your dependencies...
    ->get(MyApplication::class)
    ->run();

Out of the box, this library provides singleton and transient lifetime strategies and a variety ways of provisioning instances of specific types, as well as specifying factories for all classes in a particular namespace or implementing a specific interface. You can easily extend the default Container implementation with your own custom lifetime strategies, instance providers, or nested containers to fit your needs.

The library also provides a ContextContainer class for cascading dependency resolution down a nested context hierarchy and an Injector class for injecting dependencies and explicit parameters into a specific function or constructor.

Installation

Add suhock/dependency-injection to the require section of your project's composer.json file.

{
    "require": {
        "suhock/dependency-injection": "^0.1"
    }
}

Alternatively, use the command line from your project's root directory.

composer require "suhock/dependency-injection"

Basic Usage

The basic Container class contains methods for building the container and retrieving instances. Start by constructing an instance.

use Suhock\DependencyInjection\Container;

$container = new Container();

Next, build your container, i.e., tell the container how it should resolve specific dependencies in your application.

$container
    // Autowire the constructor
    ->addSingletonClass(MyApplication::class)

    // Manually construct an instance with factory
    ->addSingletonFactory(Logger::class, fn () => new FileLogger('myapp.log'))

    // Alias an interface to an implementing type
    ->addTransientImplementation(HttpClient::class, CurlHttpClient::class)

    // Add optional values with a mutator after autowiring the constructor
    ->addTransientClass(
        CurlHttpClient::class,
        function (CurlHttpClient $client, Logger $logger): void {
            $client->addLogger($logger);
        }
    );

Finally, call the get() method on the container to retrieve an instance of your application and run it.

$container
    ->get(MyApplication::class)
    ->handleRequest();

The container will autowire the class constructor and provide your application the instance.

class MyApplication
{
    // The constructor arguments will be provided by the container
    public function __construct(
        private readonly HttpClient $client,
        private readonly Logger $logger
    ) {
    }
}

If your application has other entry points (e.g. controllers), it might be useful to inject the container into the part of your application that invokes those entry points (e.g. a router).

$container->addSingletonInstance(Container::class, $container);

class MyRouter
{
    public function __construct(
        private readonly Container $container
    ) {
    }

    public function routeRequest(string $method, string $path): void
    {
        $controllerClassName = $this->getControllerClassName($path);
        $controller = $this->container->get($controllerClassName);
        $controller->handleRequest($method);
    }
}

Instance lifetime

The lifetime of an instance determines when the container should request a fresh instance of a class. There are two builtin lifetime strategies for classes: singleton and transient. You can also add your own custom lifetime strategies.

Singleton

Singleton instances are persisted for the lifetime of the container. When the container receives a request for a singleton instance for the first time, it will call the factory that you specified for that class, store the result, and then return it. Any time the container receives a subsequent request for that class, it will return that same instance. The default Container provides convenience methods for adding singleton factories, all starting with the prefix addSingleton.

Transient

Transient instances are never persisted and the container provides a fresh value each time an instance is requested. Each time the container receives a request for a transient instance, it will call the factory you specified for that class. The default Container provides convenience methods for adding transient factories, all starting with the prefix addTransient.

Adding dependencies to the container

There are a number of built-in ways to specify how new instances should be created.

Autowire a class
Map an interface to an implementation
Call a factory method
Provide a specific instance

If needed, can also specify your own custom instance providers.

This document uses a modified PHP syntax for conveying API information.

Autowire a class

The container will construct classes by calling the class's constructor, automatically resolving any dependencies in the constructor's parameter list.

If the class has any methods with an Autowire attribute, the container will call those methods, resolving and injecting any dependencies listed in the parameter list.

The optional $mutator callback allows additional configuration of the object after the container has initialized it. The callback must take an instance of the class as its first parameter. Additional parameters will be autowired.

callable<TClass> Mutator(TClass $instance, [object|null ...]): void;

class Container
{
    function addSingletonClass<TClass>(
        string<TClass> $className,
        Mutator<TClass>|null $mutator = null
    ): static;

    function addTransientClass<TClass>(
        string<TClass> $className,
        Mutator<TClass>|null $mutator = null
    ): static;
}

Examples

Autowiring a class constructor

In the following example, when the container provides an instance of MyService it will automatically inject all dependencies into its constructor to create an instance.

$container->addSingletonClass(MyService::class);

Using mutators to set optional properties

When the container provides instances of CurlHttpClient, after autowiring the constructor, it will also set its logger property.

$container->addTransientClass(
    CurlHttpClient::class,
    function (CurlHttpClient $obj, Logger $logger): void {
        $obj->setLogger($logger);
    }
);

Using attributes to set optional properties

When the container provides an instance of CurlHttpClient, it will see that setLogger() has an Autowire attribute and call it passing in a Logger instance resolved from the container.

use Suhock\DependencyInjection\Autowire;

class CurlHttpClient
{
    #[Autowire]
    public function setLogger(Logger $logger): void {
        $this->logger = $logger;
    }
    
    // ...
}

Map an interface to an implementation

The container will provide classes by using the instance provider of the specified implementing subclass. You must therefore also add the implementing class to the container.

class Container
{
    function addSingletonImplementation<TClass, TImpl of TClass>(
        string<TClass> $className,
        string<TImpl> $implementationClassName
    ): static;

    function addTransientImplementation<TClass, TImpl of TClass>(
        string<TClass> $className,
        string<IImpl> $implementationClassName
    ): static;
}

Examples

Mapping an interface to a concrete implementation

$container
    ->addSingletonImplementation(HttpClient::class, CurlHttpClient::class)
    ->addSingletonClass(CurlHttpClient::class);

When your application requests an instance of HttpClient, the container will see that it should actually provide an instance of CurlHttpClient. It will then autowire the CurlHttpClient constructor to provide an instance.

Chaining implementations

$container
    ->addTransientImplementation(Throwable::class, Exception::class)
    ->addTransientImplementation(Exception::class, LogicException::class)
    ->addTransientClass(LogicException::class);

When your application requests an instance of Throwable, the container will see that it should actually provide an instance of Exception. Next it will see that instances of Exception should be created using LogicException. Finally, it will provide an instance of LogicException for Throwable by autowiring its constructor. If your application instead requests an instance of Exception then the container will also provide an instance of LogicException.

Unresolved mappings

The container must know how to provide the implementation or an exception will be thrown:

$container->addSingletonClass(HttpClient::class, CurlHttpClient::class);

/*
 * The container will throw an UnresolvedDependencyException because it does
 * not know how to provide an instance of CurlHttpClient.
 */
$container->get(HttpClient::class);

Call a factory method

The container will provide class instances by requesting them from a factory method. Any parameters in the factory method will be autowired.

callable<TClass> FactoryMethod([object|null ...]): TClass;

class Container
{
    function addSingletonFactory<TClass>(
        string<TClass> $className,
        FactoryMethod<TClass> $factory
    ): static;

    function addTransientFactory<TClass>(
        string<TClass> $className,
        FactoryMethod<TClass> $factory
    ): static;
}

Examples

Inject a configuration value

$container->addSingletonFactory(
    Mailer::class,
    fn (AppConfig $config) => new Mailer($config->mailerTransport)
);

When your application requests an instance of Mailer from the container, it will call the specified factory, injecting the AppConfig dependency. The factory then manually constructs an instance, specifying the mailer transport from that config.

Inline class implementation

$container->addTransientFactory(
    Logger::class,
    fn (FileWriter $writer) => new class($writer) implements Logger {
        public function __construct(private readonly FileWriter $writer)
        {
        }

        public function log(string $message): void
        {
            $this->writer->writeLine($message);
        }
    }
);

Provide a specific instance

The container will provide a pre-constructed instance of a class.

class Container
{
    function addSingletonInstance<TClass>(
        string<TClass> $className,
        TClass $instance
    ): static;
}

Examples

Basic usage

$request = new Request($_SERVER, $_GET, $_POST, $_COOKIE);
$container->addSingletonInstance(Request::class, $request);

Anytime your application requires a Request object, the container will provide the exact same instance that was passed in with the $request variable.

Nested containers

If the container cannot find a way to provide an instance of a specific class, it will next check to see if there are any nested containers that can provide the value. Two built-in nested container implementations are provided: namespace and implementation. You can also add custom containers that implement ContainerInterface using the addContainer() method. Nested containers are searched sequentially in the order they are added.

Namespace container

Namespace containers provide an instance of the requested class if it is in the configured namespace. By default, the namespace container will autowire the constructor for all classes in the namespace.

The namespace container accepts an optional $factory parameter that specifies a method which provides instances of classes in the namespace. The factory must take the name of the class being instantiated as the first parameter. The outer container will provide any additional dependencies.

callable ClassFactory<TClass>(
    string<TClass> $className,
    object|null ...$dependencies
): TClass;

class Container
{
    function addSingletonNamespace(
        string $namespace,
        ClassFactory|null $factory = null
    ): static;

    function addTransientNamespace(
        string $namespace,
        ClassFactory|null $factory = null
    ): static;
}

Examples

$container->addSingletonNamespace('Http');

/*
 * The container will provide an instance of CurlHttpClient by autowiring the
 * constructor because the class is in the Http namespace.
 */
$curlClient = $container->get(Http\CurlHttpClient::class);

$container->addSingletonImplementation(
    Http\HttpClient::class,
    Http\CurlHttpClient::class
);

/*
 * The container will know to autowire CurlHttpClient for HttpClient because we
 * specified the interface-implementation mapping.
 */
$httpClient = $container->get(Http\HttpClient::class);

Interface container

Interface containers provide an instance of the requested class if it is a subclass of the specified interface or base class. Instances are acquired from the given factory, or by autowiring the constructor if no factory is provided. The factory must take the class name as the first parameter. The outer container will provide any additional dependencies.

callable<TClass> ImplementationFactory<TImpl of TClass>(
    string<TImpl> $className,
    [object|null ...]
): TImpl;

class Container
{
    function addSingletonInterface<TInterface>(
        string<TInterface> $className,
        ImplementationFactory<TClass>|null $factory = null
    ): static;

    function addTransientInterface<TInterface>(
        string<TInterface> $className,
        ImplementationFactory<TClass>|null $factory = null
    ): static;
}

Examples

The following example retrieves repository instances from a third-party library's container.

$container->addSingletonInterface(
    EntityNameProvider::class,
    /**
     * @template T of EntityNameProvider
     * @var class-string<T> $className
     * @return T
     */
    fn (string $className, EntityManager $em) =>
        $em->getRepository($className::getEntityName())
);

/*
 * The container will query the EntityManager for a UserRepository.
 */
$userRepository = $container->get(UserRepository::class);

class UserRepository extends EntityRepository implements EntityNameProvider
{
    public static function getEntityName(): string
    {
        return User::class;
    }
}

Attribute container

Attribute containers will provide an instance of any class that has the specified attribute. Instances are acquired from the given factory, or by autowiring the constructor if no factory is provided. The factory must take the class name as the first parameter and an attribute instance as the second. The outer container will provide any additional dependencies.

callable<TAttr> AttributeClassFactory<TClass>(
    string<TClass> $className,
    TAttr $attributeInstance,
    [object|null ...]
): TClass;

class Container
{
    function addSingletonAttribute<TAttr>(
        string<TAttr> $attributeName,
        AttributeClassFactory<TAttr>|null $factory = null
    ): static;

    function addTransientAttribute<TAttr>(
        string<TAttr> $attributeName,
        AttributeClassFactory<TAttr>|null $factory = null
    ): static;
}

Examples

The following example provides an alternative to the example under interface container section, using an attribute to designate metadata rather than an interface.

$container->addSingletonAttribute(
    EntityName::class,
    fn (string $className, EntityName $attribute, EntityManager $em) =>
        $em->getRepository($attribute->getName())
);

/*
 * The container will query the EntityManager for a UserRepository.
 */
$userRepository = $container->get(UserRepository::class);

#[EntityName(User::class)]
class UserRepository extends EntityRepository
{
}

#[Attribute(Attribute::TARGET_CLASS)]
class EntityName
{
    public function __construct(
        private readonly string $name
    ) {
    }

    public function getName(): string
    {
        return $this->name;
    }
}

Customizing the Container

Custom Lifetime Strategies

Implement LifetimeStrategy and optionally extend Container with convenience methods for your new lifetime strategy.

Custom Instance Providers

Implement InstanceProvider and add it to your container using one of the basic add methods. You can also extend Container to add convenience methods for using your new instance provider.

class Container
{
    public function add<TClass>(
        string<TClass> $className,
        LifetimeStrategy<TClass> $lifetimeStrategy,
        InstanceProvider $instanceProvider
    ): static;

    public function addSingleton<TClass>(
        string<TClass> $className,
        InstanceProvider $instanceProvider
    ): static;

    public function addTransient<TClass>(
        string<TClass> $className,
        InstanceProvider $instanceProvider
    ): static;
}

Custom Nested Containers

Implement ContainerInterface and pass into the container using one of the methods below. If your custom container needs to be able to autowire objects, you can pass in the outer container to its constructor.

callable LifetimeStrategyFactory<TClass>(
    string<TClass> $className
): LifetimeStrategy<TClass>;

class Container
{
    public function addContainer(
        ContainerInterface $container,
        LifetimeStrategyFactory $lifetimeStrategyFactory
    ): static;

    public function addSingletonContainer(
        ContainerInterface $container
    ): static;

    public function addTransientContainer(
        ContainerInterface $container
    ): static;
}

Context Container

The ContextContainer class provides a collection of named containers (contexts) that can be used for providing different construction for the same class in different parts of your application. Contexts can be named with strings or enum values.

The context container utilizes a context stack for resolving dependencies. The stack can be managed by the push() and pop() methods, or using the Context attribute on class, function, or parameter declarations.

use Suhock\DependencyInjection\Context\ContextContainerFactory;
use Suhock\DependencyInjection\Context\Context;

/*
 * Strings or enums can be used as identifiers for contexts. To help ease
 * analysis and future refactorings, enums or string-typed constants are
 * recommended.
 */
enum MyContexts {
    case Default;
    case Admin;
}

$container = ContextContainerFactory::createForDefaultContainer();

/*
 * Build the Default context's container.
 */
$container->context(MyContexts::Default)
    ->addSingletonClass(MyApplication::class)
    ->addTransientImplementation(HttpClient::class, CurlHttpClient::class)
    ->addSingletonFactory(
        Settings::class,
        fn () => JsonSettings::fromFile('default.json')
    );

/*
 * Build the Admin context's container.
 */
$container->context(MyContexts::Admin)
    ->addSingletonFactory(
        Settings::class,
        fn () => JsonSettings::fromFile('admin.json')
    );

$container
    /*
     * Make Default the default, fallback context.
     * Stack: Default
     */
    ->push(MyContexts::Default)

    /*
     * Fetch the application and run it.
     */
    ->get(MyApplication::class)
    ->run();

/*
 * Stack: Default, Admin
 *
 * The container will search the Admin context then the Default context for
 * each dependency in the following class.
 */
#[Context(MyContexts::Admin)]
class AdminEditDefaultSettingsController {
    /*
     * Stack: Default, Admin
     *
     * Since no context is explicitly specified, the stack is inherited as-is
     * from the class.
     */
    public function __construct(
        /*
         * Stack: Default, Admin
         *
         * The container will resolve $settings using the Settings factory in
         * the Admin context, since Admin is at the top of the context stack.
         */
        private readonly Settings $settings,

        /*
         * Stack: Default, Admin, Default
         *
         * The container will resolve $defaultSettings using the Settings
         * factory in the Default context, since the attribute below will
         * place Default at the top of the context stack for this parameter.
         */
        #[Context(MyContexts::Default)]
        private readonly Settings $defaultSettings,

        /*
         * Stack: Default, Admin
         *
         * The container will first attempt to resolve $httpClient using the
         * Admin context. However, since HttpClient does not exist in the
         * the Admin context, the container will resolve it using the factory
         * in the Default context.
         */
        private readonly HttpClient $httpClient
    ) {
    }
}

Dependency Injector

The library also provides a dependency injector, Injector that can be used for directly calling constructors and functions, injecting any dependencies from a container. The injector also lets you directly inject specific values for named or indexed parameters.

callable<TResult of mixed> InjectableFunction([... mixed]): TResult;

class Injector
{
    public function call<TResult>(
        InjectableFunction<TResult> $function,
        array<int|string, mixed> $params = []
    ): TResult;
    
    public function instantiate<TClass>(
        string<TClass> $className,
        array<int|string, mixed> $params = []
    ): TClass;
}

Example

The following is an example where dependencies need to be injected into a function in a controller instead of the constructor.

use Suhock\DependencyInjection\Container;
use Suhock\DependencyInjection\ContainerInjector;

// Create the container and build it
$container = new Container();
// ... build the container ...

// Create an injector backed by the container
$injector = new ContainerInjector($container);

// Fetch the application router from the container
$router = $container->get(Router::class);

// Get the appropriate controller from the request path
$controller = $router->getControllerFromRequest($_SERVER);

// Call the controller's handleGet() method, injecting the indicated parameter
// values in addition to any additional dependencies in the parameter list.
$page = $injector
    ->call(
        $controller->handleGet(...),
        map_query_to_assoc_param_array($_GET)
    )

// Then, call the render() function on the return value.
$page->render();

class ProjectListController
{
    public function handleGet(
        // Parameter below will be injected from the container.
        ProjectRepository $projectRepository,

        // Parameter below will be populated from the value provided in the
        // $injector->call() parameter array. The default value will be used if
        // the key 'filter' is not present in the array.
        string $filter = ''
    ): PageInterface {
        $projects = $projectRepository->query($filter);

        return new ProjectListPage($projects);
    }
}

interface PageInterface {
    public function render(): void;
}

Specifying dependencies

A function specifies its dependencies by listing them in its parameter list. A class specifies its dependencies by listing them in the parameter list of its constructor. Dependencies must be specified as either named object types, union types, or intersection types.

Named object types

If a dependency is specified as a named object type, the container will only provide a value if it can resolve a factory for that type.

class MyApplication
{
    public function __construct(
        private readonly HttpClient $httpClient
    ) {
    }
}

In the example above, the container will attempt to resolve an instance of HttpClient. If it cannot resolve HttpClient it will throw an ParameterResolutionException.

Nullable types

If the container cannot resolve a dependency, but the dependency is nullable, then the container will provide a null value.

class MyApplication
{
    public function __construct(
        private readonly ?HttpClient $httpClient
    ) {
    }
}

In the example above, the container will attempt to resolve an instance of HttpClient. If it cannot resolve HttpClient it will inject a null value instead.

Builtin types with default values

The container is not able to resolve builtin types. However, if the function or class takes a builtin type and that parameter specifies a default value, the default value will be used.

class MyApplication
{
    public function __construct(
        private readonly HttpClient $httpClient,
        private readonly string $homeUrl = '',
        private readonly int $timeout = 0,
        private readonly array $otherOptions = []
    ) {
    }
}

In the example above, although the container cannot resolve string, int, or array types, it will autowire the constructor with the specified default values. If you need to inject non-default values for builtin types, use a factory method.

Union types

If a dependency is specified as a union type, the container will search sequentially through all named object types in the union list. It will provide a value using the first type it is able to resolve. Builtin types are ignored.

class MyApplication
{
    public function __construct(
        private readonly HttpClient|GopherClient|string $client
    ) {
    }
}

In the example above, the container will attempt to resolve an instance of HttpClient first. If it cannot resolve HttpClient, it will attempt to resolve an instance of GopherClient. If it cannot resolve GopherClient, it will ignore string and then throw an ParameterResolutionException.

Intersection types

If a dependency is specified as an intersection type, the container will attempt to fetch an instance of each type in the list until it finds one that satisfies all the types in the list. Since an instance must be retrieved in order to test whether it is a match, the use of intersection types may be slow and could have unintended consequences if the construction of any non-matching instances have side effects.

class MyApplication
{
    public function __construct(
        private readonly HttpClient&Serializable $httpClient
    ) {
    }
}

In the example above, the container will first attempt to resolve an instance of HttpClient. If it succeeds, it will check see

Appendix

A note on the service locator pattern

The previous example resembles a service locator pattern. Please note that while the Container class is functionally equivalent to a service locator, it is usually best to avoid the service locator pattern, since it makes testing, refactoring, and reasoning about your application more difficult.

Only places in your application that invoke entry points should directly use the container. If you know the specific object type required before runtime, you should rely on the container's automatic dependency injection capabilities instead of directly invoking the container. In the prior example, the application cannot know which container to invoke until it receives an actual request, so injecting the container is necessary.

The following is an example of what not to do.

/* Do NOT do this! */

class MyApiCaller
{
    public function __construct(
        private readonly Container $container
    ) {
    }

    public function callApi(): HttpResponse
    {
        $httpClient = $this->container->get(HttpClient::class);
        return $httpClient->get('https://www.example.com/api');
    }
}

In the above example, the required type, HttpClient is known before runtime and can be requested directly by the constructor. This change will make MyClass's actual dependencies much clearer thereby making testing and refactoring far easier.

/* Do this instead! */

class MyApiCaller
{
    public function __construct(
        private readonly HttpClient $httpClient
    ) {
    }

    public function callApi(): HttpResponse
    {
        return $this->httpClient->get('https://www.example.com/api');
    }
}

Refactoring toward the dependency injection pattern

An exception to the rule against the service locator pattern might be if you are refactoring a legacy application toward the dependency injection pattern: you want to reuse the container's dependency building logic as much as possible, but there is still code where it is difficult to inject dependencies properly.

In this case, the application container can be built off a singleton instance and made available to legacy code as an intermediate step. Once you finally refactor all uses of the singleton container to use proper dependency injection, the singleton container can be removed.

/* Refactor this! */
public function myFragileBloatedFunction(...$args)
{
    // ...

    // $httpClient = new CurlHttpClient();
    // $logger = new FileLogger('myapp.log');
    // $httpClient->setLogger($logger);

    // Replaced the above duplicated construction logic with a call to the
    // container
    $httpClient = getAppContainer()->get(HttpClient::class);

    $result = $httpClient->get('https://www.example.com/api/' . $args[42]);
    // ...
}

/* Eliminate all references to the singleton container and remove this! */
function getAppContainer(): Container
{
    static $container;
    return $container ??= new Container();
}

/*
 * Build your container from the singleton container for now.
 * Replace with direct construction once refactoring is complete.
 */
$container = getAppContainer();
$container->addSingletonClass(MyApplication::class);
// ...

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Dependency Injection Library for PHP

Table of Contents

Installation

Basic Usage

Instance lifetime

Singleton

Transient

Adding dependencies to the container

Autowire a class

Examples

Autowiring a class constructor

Using mutators to set optional properties

Using attributes to set optional properties

Map an interface to an implementation

Examples

Mapping an interface to a concrete implementation

Chaining implementations

Unresolved mappings

Call a factory method

Examples

Inject a configuration value

Inline class implementation

Provide a specific instance

Examples

Basic usage

Nested containers

Namespace container

Examples

Interface container

Examples

Attribute container

Examples

Customizing the Container

Custom Lifetime Strategies

Custom Instance Providers

Custom Nested Containers

Context Container

Dependency Injector

Example

Specifying dependencies

Named object types

Nullable types

Builtin types with default values

Union types

Intersection types

Appendix

A note on the service locator pattern

Refactoring toward the dependency injection pattern