Quick notes on implementing dependency injection

Most if not all PHP frameworks utilize dependency injection. Its allowing PHP to automate supplying function parameters. In my code example below in the class Test the function test requires the User class to be passed in as a parameter. Maybe you’ll want more things like Route or maybe some kind of Registry object. Having decency injection helps reduce redundant code by instantiating the function everywhere needed.

class user {
   public $id = 1;
}

class Test {
   public static function test( User $user ) {
      return $user->id;
   }
}

Here is a VERY basic example of how to implement PHP reflection.

$controller = Test;
$method = test;
$rm = new \ReflectionMethod($controller, $method);
$parameters = [];
foreach ($rm->getParameters() as $inc => $parameter) {
// Quick example getting the parameters and
// which class that parameter location is looking for
$class_name = $parameter->getType()->getName();
// Instatiate the new class
$parameters[] = new $class_name;
}
//Call the controller and method with the parameters you were expecting
call_user_func_array([$controller, $method], $parameters);

The idea is that PHP will use reflection to look at the method you are trying to call and figure out what parameters are expected. My example is simple, you can do a lot more. The idea is to present in note style form a starting point and to present the idea in a functional way.

Here are a few links for reference:

• PHP reflection
  • http://php.net/manual/en/book.reflection.php
• PHP Reflection API: Reflection Class (1/5)
  • https://www.youtube.com/watch?v=3uaPBYG4eeQ
• Good article on what reflection class could be used for
  • http://culttt.com/2014/07/02/reflection-php/