README

Danack/Injector is a recursive dependency injector. Use it to bootstrap and wire together S.O.L.I.D., object-oriented PHP applications.

Other forks

The original library, rdlowrey/auryn is in low maintenance mode. i.e. new features are very unlikely to be added, and new releases to support new versions of PHP are not guaranteed to be timely. Notes on why some features were not added to Auryn are listed here.

There are similar libraries available at:

martin-hughes/auryn is a fork from this repo and maintains the current namespace and interfaces. It is unlikely to introduce significant new features, instead focussing on bugfixes and testing.
overclokk/auryn is a fork from this repo and maintains the current namespace and interfaces. It has added the ability to lazy instantiate dependencies using Ocramius/ProxyManager.
amphp/injector is a significant rewrite using a new namespace and slightly different interfaces, requiring you to update your code. It will introduce new features and diverge over time from this repo.

How It Works

Among other things, auryn recursively instantiates class dependencies based on the parameter type-hints specified in class constructor signatures. This requires the use of Reflection. You may have heard that "reflection is slow". Let's clear something up: anything can be "slow" if you're doing it wrong. Reflection is an order of magnitude faster than disk access and several orders of magnitude faster than retrieving information (for example) from a remote database. Additionally, each reflection offers the opportunity to cache the results if you're worried about speed. auryn caches any reflections it generates to minimize the potential performance impact.

auryn is NOT a Service Locator. DO NOT turn it into one by passing the injector into your application classes. Service Locator is an anti-pattern; it hides class dependencies, makes code more difficult to maintain and makes a liar of your API! You should only use an injector for wiring together the disparate parts of your application during your bootstrap phase.

The Guide

Basic Usage

Basic Instantiation
Injection Definitions
Type-Hint Aliasing
Non-Class Parameters
Global Parameter Definitions

Advanced Usage

Instance Sharing
Instantiation Delegates
Prepares and Setter Injection
Injecting for Execution
Dependency Resolution

Example Use Cases

Avoiding Evil Singletons
Application Bootstrapping

Requirements and Installation

Danack/Injector requires PHP 7.2 or higher.

Installation

Github

You can clone the latest Danack/Injector iteration at anytime from the github repository:

$ git clone git://github.com/danacj/injector.git

Composer

You may also use composer to include auryn as a dependency in your projects composer.json. The relevant package is rdlowrey/auryn.

Alternatively require the package using composer cli:

composer require danack/injector

Manual Download

Archived tagged release versions are also available for manual download on the project tags page

Running tests

To allow an appropriate version of PHPUnit to be installed across all of the supported versions of PHP, instead of directly depending on PHPUnit, Auryn instead depends on simple-phpunit.

After doing composer update, you need to tell simple-phpunit to install PHPUnit:

vendor/bin/simple-phpunit install

vendor/bin/simple-phpunit --version

The tests can then be run with the command:

vendor/bin/simple-phpunit

Basic Usage

To start using the injector, simply create a new instance of the Auryn\Injector ("the Injector") class:

<?php
$injector = new DI\Injector;

Basic Instantiation

If a class doesn't specify any dependencies in its constructor signature there's little point in using the Injector to generate it. However, for the sake of completeness consider that you can do the following with equivalent results:

<?php
$injector = new DI\Injector;
$obj1 = new SomeNamespace\MyClass;
$obj2 = $injector->make('SomeNamespace\MyClass');

var_dump($obj2 instanceof SomeNamespace\MyClass); // true

Concrete Type-hinted Dependencies

If a class only asks for concrete dependencies you can use the Injector to inject them without specifying any injection definitions. For example, in the following scenario you can use the Injector to automatically provision MyClass with the required SomeDependency and AnotherDependency class instances:

<?php
class SomeDependency {}

class AnotherDependency {}

class MyClass {
    public $dep1;
    public $dep2;
    public function __construct(SomeDependency $dep1, AnotherDependency $dep2) {
        $this->dep1 = $dep1;
        $this->dep2 = $dep2;
    }
}

$injector = new DI\Injector;
$myObj = $injector->make('MyClass');

var_dump($myObj->dep1 instanceof SomeDependency); // true
var_dump($myObj->dep2 instanceof AnotherDependency); // true

Recursive Dependency Instantiation

One of the Injector's key attributes is that it recursively traverses class dependency trees to instantiate objects. This is just a fancy way of saying, "if you instantiate object A which asks for object B, the Injector will instantiate any of object B's dependencies so that B can be instantiated and provided to A". This is perhaps best understood with a simple example. Consider the following classes in which a Car asks for Engine and the Engine class has concrete dependencies of its own:

<?php
class Car {
    private $engine;
    public function __construct(Engine $engine) {
        $this->engine = $engine;
    }
}

class Engine {
    private $sparkPlug;
    private $piston;
    public function __construct(SparkPlug $sparkPlug, Piston $piston) {
        $this->sparkPlug = $sparkPlug;
        $this->piston = $piston;
    }
}

$injector = new DI\Injector;
$car = $injector->make('Car');
var_dump($car instanceof Car); // true

Injection Definitions

You may have noticed that the previous examples all demonstrated instantiation of classes with explicit, type-hinted, concrete constructor parameters. Obviously, many of your classes won't fit this mold. Some classes will type-hint interfaces and abstract classes. Some will specify scalar parameters which offer no possibility of type-hinting in PHP. Still other parameters will be arrays, etc. In such cases we need to assist the Injector by telling it exactly what we want to inject.

Defining Class Names for Constructor Parameters

Let's look at how to provision a class with non-concrete type-hints in its constructor signature. Consider the following code in which a Car needs an Engine and Engine is an interface:

<?php
interface Engine {}

class V8 implements Engine {}

class Car {
    private $engine;
    public function __construct(Engine $engine) {
        $this->engine = $engine;
    }
}

To instantiate a Car in this case, we simply need to define an injection definition for the class ahead of time:

<?php
$injector = new DI\Injector;
$injector->define('Car', ['engine' => 'V8']);
$car = $injector->make('Car');

var_dump($car instanceof Car); // true

The most important points to notice here are:

A custom definition is an array whose keys match constructor parameter names
The values in the definition array represent the class names to inject for the specified parameter key

Because the Car constructor parameter we needed to define was named $engine, our definition specified an engine key whose value was the name of the class (V8) that we want to inject.

Custom injection definitions are only necessary on a per-parameter basis. For example, in the following class we only need to define the injectable class for $arg2 because $arg1 specifies a concrete class type-hint:

<?php
class MyClass {
    private $arg1;
    private $arg2;
    public function __construct(SomeConcreteClass $arg1, SomeInterface $arg2) {
        $this->arg1 = $arg1;
        $this->arg2 = $arg2;
    }
}

$injector = new DI\Injector;
$injector->define('MyClass', ['arg2' => 'SomeImplementationClass']);

$myObj = $injector->make('MyClass');

NOTE: Injecting instances where an abstract class is type-hinted works in exactly the same way as the above examples for interface type-hints.

Using Existing Instances in Injection Definitions

Injection definitions may also specify a pre-existing instance of the requisite class instead of the string class name:

<?php
interface SomeInterface {}

class SomeImplementation implements SomeInterface {}

class MyClass {
    private $dependency;
    public function __construct(SomeInterface $dependency) {
        $this->dependency = $dependency;
    }
}

$injector = new DI\Injector;
$dependencyInstance = new SomeImplementation;
$injector->define('MyClass', [':dependency' => $dependencyInstance]);

$myObj = $injector->make('MyClass');

var_dump($myObj instanceof MyClass); // true

NOTE: Since this define() call is passing raw values (as evidenced by the colon : usage), you can achieve the same result by omitting the array key(s) and relying on parameter order rather than name. Like so: $injector->define('MyClass', [$dependencyInstance]);

Specifying Injection Definitions On the Fly

You may also specify injection definitions at call-time with Auryn\Injector::make. Consider:

<?php
interface SomeInterface {}

class SomeImplementationClass implements SomeInterface {}

class MyClass {
    private $dependency;
    public function __construct(SomeInterface $dependency) {
        $this->dependency = $dependency;
    }
}

$injector = new DI\Injector;
$myObj = $injector->make('MyClass', ['dependency' => 'SomeImplementationClass']);

var_dump($myObj instanceof MyClass); // true

The above code shows how even though we haven't called the Injector's define method, the call-time specification allows us to instantiate MyClass.

NOTE: on-the-fly instantiation definitions will override a pre-defined definition for the specified class, but only in the context of that particular call to Auryn\Injector::make.

Type-Hint Aliasing

Programming to interfaces is one of the most useful concepts in object-oriented design (OOD), and well-designed code should type-hint interfaces whenever possible. But does this mean we have to assign injection definitions for every class in our application to reap the benefits of abstracted dependencies? Thankfully the answer to this question is, "NO." The Injector accommodates this goal by accepting "aliases". Consider:

<?php
interface Engine {}
class V8 implements Engine {}
class Car {
    private $engine;
    public function __construct(Engine $engine) {
        $this->engine = $engine;
    }
}

$injector = new DI\Injector;

// Tell the Injector class to inject an instance of V8 any time
// it encounters an Engine type-hint
$injector->alias('Engine', 'V8');

$car = $injector->make('Car');
var_dump($car instanceof Car); // bool(true)

In this example we've demonstrated how to specify an alias class for any occurrence of a particular interface or abstract class type-hint. Once an implementation is assigned, the Injector will use it to provision any parameter with a matching type-hint.

IMPORTANT: If an injection definition is defined for a parameter covered by an implementation assignment, the definition takes precedence over the implementation.

Non-Class Parameters

All of the previous examples have demonstrated how the Injector class instantiates parameters based on type-hints, class name definitions and existing instances. But what happens if we want to inject a scalar or other non-object variable into a class? First, let's establish the following behavioral rule:

IMPORTANT: The Injector assumes all named-parameter definitions are class names by default.

If you want the Injector to treat a named-parameter definition as a "raw" value and not a class name, you must prefix the parameter name in your definition with a colon character :. For example, consider the following code in which we tell the Injector to share a PDO database connection instance and define its scalar constructor parameters:

<?php
$injector = new DI\Injector;
$injector->share('PDO');
$injector->define('PDO', [
    ':dsn' => 'mysql:dbname=testdb;host=127.0.0.1',
    ':username' => 'dbuser',
    ':passwd' => 'dbpass'
]);

$db = $injector->make('PDO');

The colon character preceding the parameter names tells the Injector that the associated values ARE NOT class names. If the colons had been omitted above, auryn would attempt to instantiate classes of the names specified in the string and an exception would result. Also, note that we could just as easily specified arrays or integers or any other data type in the above definitions. As long as the parameter name is prefixed with a :, auryn will inject the value directly without attempting to instantiate it.

NOTE: As mentioned previously, since this define() call is passing raw values, you may opt to assign the values by parameter order rather than name. Since PDO's first three parameters are $dsn, $username, and $password, in that order, you could accomplish the same result by leaving out the array keys, like so: $injector->define('PDO', ['mysql:dbname=testdb;host=127.0.0.1', 'dbuser', 'dbpass']);

Global Parameter Definitions

Sometimes applications may reuse the same value everywhere. However, it can be a hassle to manually specify definitions for this sort of thing everywhere it might be used in the app. auryn mitigates this problem by exposing the Injector::defineParam() method. Consider the following example ...

<?php
$myUniversalValue = 42;

class MyClass {
    public $myValue;
    public function __construct($myValue) {
        $this->myValue = $myValue;
    }
}

$injector = new DI\Injector;
$injector->defineParam('myValue', $myUniversalValue);
$obj = $injector->make('MyClass');
var_dump($obj->myValue === 42); // bool(true)

Because we specified a global definition for myValue, all parameters that are not in some other way defined (as below) that match the specified parameter name are auto-filled with the global value. If a parameter matches any of the following criteria the global value is not used:

A parameter type
A predefined injection definition
A custom call time definition

Advanced Usage

Instance Sharing

One of the more ubiquitous plagues in modern OOP is the Singleton anti-pattern. Coders looking to limit classes to a single instance often fall into the trap of using static Singleton implementations for things like configuration classes and database connections. While it's often necessary to prevent multiple instances of a class, the Singleton method spells death to testability and should generally be avoided. Auryn\Injector makes sharing class instances across contexts a triviality while allowing maximum testability and API transparency.

Let's consider how a typical problem facing object-oriented web applications is easily solved by wiring together your application using auryn. Here, we want to inject a single database connection instance across multiple layers of an application. We have a controller class that asks for a DataMapper that requires a PDO database connection instance:

<?php
class DataMapper {
    private $pdo;
    public function __construct(PDO $pdo) {
        $this->pdo = $pdo;
    }
}

class MyController {
    private $mapper;
    public function __construct(DataMapper $mapper) {
        $this->mapper = $mapper;
    }
}

$db = new PDO('mysql:host=localhost;dbname=mydb', 'user', 'pass');

$injector = new DI\Injector;
$injector->share($db);

$myController = $injector->make('MyController');

In the above code, the DataMapper instance will be provisioned with the same PDO database connection instance we originally shared. This example is contrived and overly simple, but the implication should be clear:

By sharing an instance of a class, Auryn\Injector will always use that instance when provisioning classes that type-hint the shared class.

A Simpler Example

Let's look at a simple proof of concept:

<?php
class Person {
    public $name = 'John Snow';
}

$injector = new DI\Injector;
$injector->share('Person');

$person = $injector->make('Person');
var_dump($person->name); // John Snow

$person->name = 'Arya Stark';

$anotherPerson = $injector->make('Person');
var_dump($anotherPerson->name); // Arya Stark
var_dump($person === $anotherPerson); // bool(true) because it's the same instance!

Defining an object as shared will store the provisioned instance in the Injector's shared cache and all future requests to the provider for an injected instance of that class will return the originally created object. Note that in the above code, we shared the class name (Person) instead of an actual instance. Sharing works with either a class name or an instance of a class. The difference is that when you specify a class name, the Injector will cache the shared instance the first time it is asked to create it.

NOTE: Once the Injector caches a shared instance, call-time definitions passed to Auryn\Injector::make will have no effect. Once shared, an instance will always be returned for instantiations of its type until the object is un-shared or refreshed:

Instantiation Delegates

Often factory classes/methods are used to prepare an object for use after instantiation. auryn allows you to integrate factories and builders directly into the injection process by specifying callable instantiation delegates on a per-class basis. Let's look at a very basic example to demonstrate the concept of injection delegates:

<?php
class MyComplexClass {
    public $verification = false;
    public function doSomethingAfterInstantiation() {
        $this->verification = true;
    }
}

$complexClassFactory = function() {
    $obj = new MyComplexClass;
    $obj->doSomethingAfterInstantiation();

    return $obj;
};

$injector = new DI\Injector;
$injector->delegate('MyComplexClass', $complexClassFactory);

$obj = $injector->make('MyComplexClass');
var_dump($obj->verification); // bool(true)

In the above code we delegate instantiation of the MyComplexClass class to a closure, $complexClassFactory. Once this delegation is made, the Injector will return the results of the specified closure when asked to instantiate MyComplexClass.

Available Delegate Types

Any valid PHP callable may be registered as a class instantiation delegate using Auryn\Injector::delegate. Additionally you may specify the name of a delegate class that specifies an __invoke method and it will be automatically provisioned and have its __invoke method called at delegation time. Instance methods from uninstantiated classes may also be specified using the ['NonStaticClassName', 'factoryMethod'] construction. For example:

<?php
class SomeClassWithDelegatedInstantiation {
    public $value = 0;
}
class SomeFactoryDependency {}
class MyFactory {
    private $dependency;
    function __construct(SomeFactoryDependency $dep) {
        $this->dependency = $dep;
    }
    function __invoke() {
        $obj = new SomeClassWithDelegatedInstantiation;
        $obj->value = 1;
        return $obj;
    }
    function factoryMethod() {
        $obj = new SomeClassWithDelegatedInstantiation;
        $obj->value = 2;
        return $obj;
    }
}

// Works because MyFactory specifies a magic __invoke method
$injector->delegate('SomeClassWithDelegatedInstantiation', 'MyFactory');
$obj = $injector->make('SomeClassWithDelegatedInstantiation');
var_dump($obj->value); // int(1)

// This also works
$injector->delegate('SomeClassWithDelegatedInstantiation', 'MyFactory::factoryMethod');
$obj = $injector->make('SomeClassWithDelegatedInstantiation');
$obj = $injector->make('SomeClassWithDelegatedInstantiation');
var_dump($obj->value); // int(2)

Prepares and Setter Injection

Constructor injection is almost always preferable to setter injection. However, some APIs require additional post-instantiation mutations. auryn accommodates these use cases with its Injector::prepare() method. Users may register any class or interface name for post-instantiation modification. Consider:

<?php

class MyClass {
    public $myProperty = 0;
}

$injector->prepare('MyClass', function($myObj, $injector) {
    $myObj->myProperty = 42;
});

$myObj = $injector->make('MyClass');
var_dump($myObj->myProperty); // int(42)

While the above example is contrived, the usefulness should be clear.

Additionally, the prepare method is able to replace the object being prepared with another of the same or descendant type:

<?php

class FooGreeter {
    public function getMessage(): string {
        return "Hello, I am foo.";
    }
}

class BarGreeter extends FooGreeter {
    public function getMessage(): string {
        return "Hello, I am bar.";
    }
}

$injector = new \DI\Injector();

$injector->prepare(FooGreeter::class, function($myObj, $injector) {
    return new BarGreeter();
});

$myObj = $injector->make(FooGreeter::class);
echo $myObj->getMessage(); // Output is: "Hello, I am bar."

The usefulness of this is much less clear.

Any value returned that is not the same or descendant type will be ignored.

Injecting for Execution

In addition to provisioning class instances using constructors, auryn can also recursively instantiate the parameters of any valid PHP callable. The following examples all work:

<?php
$injector = new DI\Injector;
$injector->execute(function(){});
$injector->execute([$objectInstance, 'methodName']);
$injector->execute('globalFunctionName');
$injector->execute('MyStaticClass::myStaticMethod');
$injector->execute(['MyStaticClass', 'myStaticMethod']);
$injector->execute(['MyChildStaticClass', 'parent::myStaticMethod']);
$injector->execute('ClassThatHasMagicInvoke');
$injector->execute($instanceOfClassThatHasMagicInvoke);
$injector->execute('MyClass::myInstanceMethod');

Additionally, you can pass in the name of a class for a non-static method and the injector will automatically provision an instance of the class (subject to any definitions or shared instances already stored by the injector) before provisioning and invoking the specified method:

<?php
class Dependency {}
class AnotherDependency {}
class Example {
    function __construct(Dependency $dep){}
    function myMethod(AnotherDependency $arg1, $arg2) {
        return $arg2;
    }
}

$injector = new DI\Injector;

// outputs: int(42)
var_dump($injector->execute('Example::myMethod', $args = [':arg2' => 42]));

Injector::make and Injector::execute custom args

The args parameter in both of Injector::make($name, array $args = array()) and Injector::execute($callableOrMethodStr, array $args = array())) allow you to pass in a bespoke set of parameters to be used during the creation/execution.

The rules for how those injector args are used is as follows.

Given a parameter named 'foo' at parameter position 'i' which has a type of 'bar', for the thing being created/executed:

If an integer indexed key 'i' is present (i.e. does $args[$i] exist?) then use the value of $args[$i] directly for that parameter.
If an string indexed key 'foo' is present (i.e. does $args['foo'] exist?) then use the value of $args['foo'] for that parameter.
If a string indexed key Injector::A_DELEGATE . 'foo' is present (i.e. does $args['+foo'] exist?) then interpret $args['+' . $i] as a delegate callable to be invoked, and the return value to be used for that parameter.
If a string indexed key Injector::A_DEFINE . 'foo' is present (i.e. does $args['@foo'] exist?) then interpret $args['+' . $i] as an array with

$params = [
    PrefixDefineDependency::class,
    [Injector::A_RAW . 'message' => $message]
];

$object = $injector->make(
    PrefixDefineTest::class,
    [Injector::A_DEFINE . 'pdd' => $params]
);

i.e. when the injector is making the class 'PrefixDefineTest which has a dependency on the class PrefixDefineDependency, which is named as parameter 'pdd' in the constructor, use the values in the array $params[1], to instantiate the PrefixDefineDependency class.

If a string indexed key Injector::A_DEFINE . '+foo' is present (i.e. does $args[':foo'] exist?) then interpret $args['+' . $i] as a value to be used a parameter defined by name. This is similar behaviour to $injector->define('foo', 'bar');
Try to build the arg through the normal Auryn argument building process.

Dependency Resolution

Auryn\Injector resolves dependencies in the following order:

If a shared instance exists for the class in question, the shared instance will always be returned
If a delegate callable is assigned for a class, its return result will always be used
If a call-time definition is passed to Auryn\Injector::make, that definition will be used
If a pre-defined definition exists, it will be used
If a dependency is type-hinted, the Injector will recursively instantiate it subject to any implementations or definitions
If no type-hint exists and the parameter has a default value, the default value is injected
If a global parameter value is defined that value is used
Throw an exception because you did something stupid

Example Use Cases

Dependency Injection Containers (DIC) are generally misunderstood in the PHP community. One of the primary culprits is the misuse of such containers in the mainstream application frameworks. Often, these frameworks warp their DICs into Service Locator anti-patterns. This is a shame because a good DIC should be the exact opposite of a Service Locator.

auryn Is NOT A Service Locator!

There's a galaxy of differences between using a DIC to wire together your application versus passing the DIC as a dependency to your objects (Service Locator). Service Locator (SL) is an anti-pattern -- it hides class dependencies, makes code difficult to maintain and makes a liar of your API.

When you pass a SL into your constructors it makes it difficult to determine what the class dependencies really are. A House object depends on Door and Window objects. A House object DOES NOT depend on an instance of ServiceLocator regardless of whether the ServiceLocator can provide Door and Window objects.

In real life you wouldn't build a house by transporting the entire hardware store (hopefully) to the construction site so you can access any parts you need. Instead, the foreman (__construct()) asks for the specific parts that will be needed (Door and Window) and goes about procuring them. Your objects should function in the same way; they should ask only for the specific dependencies required to do their jobs. Giving the House access to the entire hardware store is at best poor OOP style and at worst a maintainability nightmare. The takeaway here is this:

IMPORTANT: do not use auryn like a Service Locator!

Avoiding Evil Singletons

A common difficulty in web applications is limiting the number of database connection instances. It's wasteful and slow to open up new connections each time we need to talk to a database. Unfortunately, using singletons to limit these instances makes code brittle and hard to test. Let's see how we can use auryn to inject the same PDO instance across the entire scope of our application.

Say we have a service class that requires two separate data mappers to persist information to a database:

<?php

class HouseMapper {
    private $pdo;
    public function __construct(PDO $pdo) {
        $this->pdo = $pdo;
    }
    public function find($houseId) {
        $query = 'SELECT * FROM houses WHERE houseId = :houseId';

        $stmt = $this->pdo->prepare($query);
        $stmt->bindValue(':houseId', $houseId);

        $stmt->setFetchMode(PDO::FETCH_CLASS, 'Model\\Entities\\House');
        $stmt->execute();
        $house = $stmt->fetch(PDO::FETCH_CLASS);

        if (false === $house) {
            throw new RecordNotFoundException(
                'No houses exist for the specified ID'
            );
        }

        return $house;
    }

    // more data mapper methods here ...
}

class PersonMapper {
    private $pdo;
    public function __construct(PDO $pdo) {
        $this->pdo = $pdo;
    }
    // data mapper methods here
}

class SomeService {
    private $houseMapper;
    private $personMapper;
    public function __construct(HouseMapper $hm, PersonMapper $pm) {
        $this->houseMapper = $hm;
        $this->personMapper = $pm;
    }
    public function doSomething() {
        // do something with the mappers
    }
}

In our wiring/bootstrap code, we simply instantiate the PDO instance once and share it in the context of the Injector:

<?php
$pdo = new PDO('sqlite:some_sqlite_file.db');
$pdo->setAttribute(PDO::ATTR_ERRMODE, PDO::ERRMODE_EXCEPTION);

$injector = new DI\Injector;

$injector->share($pdo);
$mapper = $injector->make('SomeService');

In the above code, the DIC instantiates our service class. More importantly, the data mapper classes it generates to do so are injected with the same database connection instance we originally shared.

Of course, we don't have to manually instantiate our PDO instance. We could just as easily seed the container with a definition for how to create the PDO object and let it handle things for us:

<?php
$injector->define('PDO', [
    ':dsn' => 'sqlite:some_sqlite_file.db'
]);
$injector->share('PDO');
$service = $injector->make('SomeService');

In the above code, the injector will pass the string definition as the $dsn argument in the PDO::__construct method and generate the shared PDO instance automatically only if one of the classes it instantiates requires a PDO instance!

App-Bootstrapping

DICs should be used to wire together the disparate objects of your application into a cohesive functional unit (generally at the bootstrap or front-controller stage of the application). One such usage provides an elegant solution for one of the thorny problems in object-oriented (OO) web applications: how to instantiate classes in a routed environment where the dependencies are not known ahead of time.

Consider the following front controller code whose job is to:

Load a list of application routes and pass them to the router
Generate a model of the client's HTTP request
Route the request instance given the application's route list
Instantiate the routed controller and invoke a method appropriate to the HTTP request

<?php

define('CONTROLLER_ROUTES', '/hard/path/to/routes.xml');

$routeLoader = new RouteLoader();
$routes = $routeLoader->loadFromXml(CONTROLLER_ROUTES);
$router = new Router($routes);

$requestDetector = new RequestDetector();
$request = $requestDetector->detectFromSuperglobal($_SERVER);

$requestUri = $request->getUri();
$requestMethod = strtolower($request->getMethod());

$injector = new DI\Injector;
$injector->share($request);

try {
    if (!$controllerClass = $router->route($requestUri, $requestMethod)) {
        throw new NoRouteMatchException();
    }

    $controller = $injector->make($controllerClass);
    $callableController = array($controller, $requestMethod);

    if (!is_callable($callableController)) {
        throw new MethodNotAllowedException();
    } else {
        $callableController();
    }

} catch (NoRouteMatchException $e) {
    // send 404 response
} catch (MethodNotAllowedException $e) {
    // send 405 response
} catch (Exception $e) {
    // send 500 response
}

And elsewhere we have various controller classes, each of which ask for their own individual dependencies:

<?php

class WidgetController {
    private $request;
    private $mapper;
    public function __construct(Request $request, WidgetDataMapper $mapper) {
        $this->request = $request;
        $this->mapper = $mapper;
    }
    public function get() {
        // do something for HTTP GET requests
    }
    public function post() {
        // do something for HTTP POST requests
    }
}

In the above example the auryn DIC allows us to write fully testable, fully OO controllers that ask for their dependencies. Because the DIC recursively instantiates the dependencies of objects it creates we have no need to pass around a Service Locator. Additionally, this example shows how we can eliminate evil Singletons using the sharing capabilities of the auryn DIC. In the front controller code, we share the request object so that any classes instantiated by the Auryn\Injector that ask for a Request will receive the same instance. This feature not only helps eliminate Singletons, but also the need for hard-to-test static properties.

When app-bootstrapping by Auryn is not possible

Sometimes, the initialisation of the application is outside of your control. One example would be writing plugins for Wordpress, where Wordpress is initialising your plugin, not the other way round.

You can still use Auryn by using a function to make a single instance of the injector:

function getInjector()
{
    static $injector = null;
	if ($injector == null) {
		$injector = new \DI\Injector();
		// Do injector defines/shares/aliases/delegates here
	}

    return $injector;
}

Advanced patterns

"Variadic" dependencies

Sometimes your code might need a variable number of objects to be passed as a parameter.

class Foo {
  public function __construct(Repository ...$repositories) {
  // do stuff with $repositories
  }
}

In this scenario $repositories does not represent a single simple variable, instead $repositories represents a complex type.

As Auryn works by defining rules about types, Auryn isn't able to do injection and so you'll need to use a more advanced technique to be able to inject.

Variadics using delegate function

The simplest way to support being able to create objects that themselves have variadic dependencies, is to use a delegate function to create it:

function createFoo(RepositoryLocator $repoLocator)
{
    // Or whatever code is needed to find the repos.
    $repositories = $repoLocator->getRepos('Foo');

    return new Foo($repositories);
}

$injector->delegate('Foo', 'createFoo');

This should only take a few moments to write the code for, but it has the downside that it moves some application logic into injector.

Variadics using factory classes

A very slightly longer way to create objects that themselves have variadic dependencies, is to refactor them to use a factory object to get the dependencies:

class RepositoryList
{
    /**
    * @return Repository[]
    */
    public function getRelevantRepositories() {
        // do stuff with $repositories
    }
}

class Foo {
    public function __construct(RepositoryList $respositoryList)
    {
        $repositories = $respositoryList->getRelevantRepositories();

        // error handling goes here

        // do stuff with $repositories
    }
}

This probably a slightly better approach than using the delegate method, as it avoids business/application logic being in the dependency injector, and give you an appropriate place inside your own code to handle errors.

Context objects and multiple instances of the same types

Sometimes you might need to have multiple instances of the same type.

For example, a background job that moves data from the live database, into the archive database might need to have two instances of a DB class injected

class DataArchiver
{
    public function __construct(private PDO $live_db, private PDO $archive_db)
    {
    }
}

This can be worked around by using the type system to create more specific types:

class LivePDO extends PDO {}
class ArchivePDO extends PDO {}

class DataArchiver
{
    public function __construct(private LivePDO $live_db, private ArchivePDO $archive_db)
    {
    }
}

The more specific types can then be created through Auryn, by configuring an appropriate delegate function for each of them

This approach works, and is actually a reasonable one for small projects, there is an more comprehensive approach that is more appropriate for larger projects.

Encapsulated contexts

Or to give it the full name, using the 'Encapsulated context pattern'](https://www.allankelly.net/static/patterns/encapsulatecontext.pdf).

The short description of 'Encapsulated contexts' is that you create specific types that hold all of the needed types for a particular business/domain problem, and allow you to wire them up specifically:

class DataArchiverContext
{
    public function __construct(
        private PDO $live_db,
        private PDO $archive_db
    ) {

    public function get_live_db(): PDO
    {
        return $this->live_db;
    }

    public function get_archive_db(): PDO
    {
        return $this->archive_db;
    }
}

class DataArchiver
{
    public function __construct(private DataArchiverContext $dac)
    {
    }
}

function createDataArchiver()
{
    return new DataArchiver(
        createLiveDB(),
        createArchiveDB()
    );
}

$injector->delegate(DataArchiverContext::class, 'createDataArchiver');

Encapsulated contexts makes your code far easier to reason about. You can see:

where a particular context is used.
what types are in it.
how it is created, including any special rules for it.

This makes maintaining and reasoning about large programs easier.

Running tests and benchmarks

Running tests

As there is no single version of PHPUnit that works on all the versions of PHP that Auryn supports, we use simple-phpunit to install an appropriate version of PHP.

After running the composer update to get the latest dependencies, run:

php vendor/bin/simple-phpunit install

to make simple-phpunit install PHPUnit. The tests can then be with with the command:

php vendor/bin/simple-phpunit

simple-phpunit accepts PHPUnit commandline options and passes them through to PHPUnit e.g. php php vendor/bin/simple-phpunit --group wip to only run the tests tagged as being part of group 'wip'.

Running benchamarks

We use PHPBench to allow checking performance gains/regressions when making code changes. The simplest way to use it is as follows:

Create a benchmark baseline by running:

vendor/bin/phpbench run --tag=benchmark_original --retry-threshold=5 --iterations=10

Apply your code changes.
Run a benchmark, and compare the results to the 'benchmark_original' by running:

vendor/bin/phpbench run --report=aggregate --ref=benchmark_original --retry-threshold=5 --iterations=10

danack / injector

Maintainers

Details

README

Other forks

How It Works

The Guide

Requirements and Installation

Installation

Github

Composer

Manual Download

Running tests

Basic Usage

Basic Instantiation

Concrete Type-hinted Dependencies

Recursive Dependency Instantiation

Injection Definitions

Defining Class Names for Constructor Parameters

Using Existing Instances in Injection Definitions

Specifying Injection Definitions On the Fly

Type-Hint Aliasing

Non-Class Parameters

Global Parameter Definitions

Advanced Usage

Instance Sharing

A Simpler Example

Instantiation Delegates

Available Delegate Types

Prepares and Setter Injection

Injecting for Execution

Injector::make and Injector::execute custom args

Dependency Resolution

Example Use Cases

auryn Is NOT A Service Locator!

Avoiding Evil Singletons

App-Bootstrapping

When app-bootstrapping by Auryn is not possible

Advanced patterns

"Variadic" dependencies

Variadics using delegate function

Variadics using factory classes

Context objects and multiple instances of the same types

Encapsulated contexts

Running tests and benchmarks

Running tests

Running benchamarks