Yii2 Dependency Injection Container - interface registration not resolving dependent object instance - php

Question

In the Yii2 Guide it describes various methods of Registering Dependencies with the Dependency Injection Container. See here: https://www.yiiframework.com/doc/guide/2.0/en/concept-di-container#registering-dependencies
// register an interface
// When a class depends on the interface, the corresponding class
// will be instantiated as the dependent object
$container->set('yii\mail\MailInterface', 'yii\swiftmailer\Mailer');
So I have tested this and it doesn't appear to function as described because the registered mapping of an interface to class does not resolve in the created object. See my test code examples below...
Custom Test Class Requiring Dependency Interface:
namespace api\components\Test;
class DependencyTest
{
public function __construct(\api\components\Test\DependencyInterface $dependency, $config = [])
{
echo '<pre>';
echo '$dependency->getSummary() ' . print_r($dependency->getSummary(), true);
echo '</pre>';
exit;
parent::__construct($config);
}
}
Custom Dependency Interface:
namespace api\components\Test;
interface DependencyInterface
{
public function getSummary();
}
Custom Dependency Class:
namespace api\components\Test;
class DependencyClass implements DependencyInterface
{
public function getSummary() {
return [
'currentClassMethod' => __METHOD__,
];
}
}
In Controller:
$container = new \yii\di\Container;
$container->set('\api\components\Test\DependencyInterface', '\api\components\Test\DependencyClass');
try {
$dependencyTest = $container->get('\api\components\Test\DependencyTest');
} catch (\Exception $e) {
echo '<pre>';
echo '$e->getMessage() ' . print_r($e->getMessage(), true);
echo '</pre>';
die();
}
Running this in the controller, I see the following response:
$e->getMessage() Can not instantiate api\components\Test\DependencyInterface.
Why does DI container not resolve the registered interface to the mapped class (DependencyClass) and inject an instance of this into the constructor of DependencyTest? From the generated exception, it would seem that it is ignoring this and trying to instantiate the interface itself.
Is the guide simply misleading here? Do I have to additionally do this?
$dependencyTest = $container->get(
'\api\components\Test\DependencyTest',
// constructor params
[$container->get('\api\components\Test\DependencyInterface')]
);
Now it does work, but it seems to destroy the whole objective of using this DI container in the first place instead of simply instantiating in a regular php way!