Dependency Injection

WellRESTed strives to play nicely with other code and not force developers into using any specific libraries or frameworks. As such, WellRESTed does not provide a dependency injection container, nor does it require you to use a specific container (or any).

This section describes the recommended way of using WellRESTed with Pimple, a common dependency injection container for PHP.

Imaging we have a FooHandler that depends on a BarInterface, and BazInterface. Our handler looks something like this:

class FooHandler implements RequestHandlerInterface
{
    private $bar;
    private $baz;

    public function __construct(BarInterface $bar, BazInterface $bar)
    {
        $this->bar = $bar;
        $this->baz = $baz;
    }

    public function handle(ServerRequestInterface $request): ResponseInterface
    {
        // Do something with the bar and baz and return a response...
        // ...
    }
}

We can register the handler and these dependencies in a Pimple service provider.

class MyServiceProvider implements ServiceProviderInterface
{
    public function register(Container $c)
    {
        // Register the Bar and Baz as services.
        $c['bar'] = function ($c) {
            return new Bar();
        };
        $c['baz'] = function ($c) {
            return new Baz();
        };

        // Register the Handler as a protected function. When you use
        // protect, Pimple returns the function itself instead of the return
        // value of the function.
        $c['fooHandler'] = $c->protect(function () use ($c) {
            return new FooHandler($c['bar'], $c['baz']);
        });
    }
}

By “protecting” the fooHandler service, we are delaying the instantiation of the FooHandler, the Bar, and the Baz until the handler needs to be dispatched. This works because we’re not passing instance of FooHandler when we register this with a router, we’re passing a function to it that does the instantiation on demand.