rawebone/injector

A library providing a low level service injection API

1.0.3 2014-07-13 19:51 UTC

Requires (Dev)

• phpspec/phpspec: 2.1.x-dev

MIT

• Nick Rawe

README

Injector provides a low level service injection system partly influenced by that found in AngularJS. The idea is somewhat similar to dependency injection although it actually injects services - the difference between the two is nuanced but loosely: DI works based on types, overriding on a per class definition whereas services work on names.

For example, in a DI scenario these two log instances will be the same (without some other configuration):

use Psr\Log\LoggerInterface;

interface Injectable
{
    function __construct(LoggerInterface $logA, LoggerInterface $logB);
}

While DI and configuration of this kind is useful in very large applications for smaller more concise applications the cost of implementation is higher as it is normally more complex. As such in these smaller applications, SL can normally wield more of a benefit as you still get lazy loading of instances and the ability to easily change a definition.

However traditional SL systems have a drawback in that they work on a pull system:

$container["logA"] = function ($container) { return new MyLogger($container["fileA"]); };
$container["logB"] = function ($container) { return new MyOtherLogger($container["fileB"]); };

$container["logB"]->warning("blah");

As such your application, in addition to some syntax and bloat from the DSL, will also not be as succinct (in my humble opinion).

This library provides a low level mechanism for injecting services into instances to clear some of the bloat, in addition to some low level utilities for working with functions and function signatures.

The Injector Approach

use Rawebone\Injector\Injector;

$injector = new Injector();

// By default, the injector will resolve to any callable
// with the name given as a broad brush approach:
function my_service()
{
    return new stdClass();
}

// Injection can be handled automatically by passing through
// a callable to the library

$injector->inject(function ($my_service)
{
    var_dump($my_service); // stdClass
});

// Injection can be handled manually by returning the service by name:

$my_service = $injector->service("my_service");

// Or simply getting arguments for the callable:

$args = $injector->argsFor(function ($my_service) {});
var_dump($args); // array("my_service" => stdClass);

As stated, the "resolve anything callable to a service name" is a broad brush tactic but it doesn't give us what we normally want. As such implementers can specify their own behaviour by implementing the Rawebone\Injector\ResolverInterface which takes in a service name and returns a value to be injected.

The library also provides a more common solution to the problem through the Rawebone\Injector\RegisterResolver:

<?php

$resolver = new Rawebone\Injector\RegisterResolver();
$resolver->register("serviceA", function () { return new MyService(); });
$resolver->register("serviceB", new \stdClass());

$resolver->registerMany(array(
    "serviceC" => new \stdClass(),
    "serviceD" => function () { return new MyService(); }
));

$injector->resolver($resolver);

License

MIT, please see the included document for details.