Why Do I need an Assignment Operator in This Statement? - php

Question

I'm playing around with some different design patterns to teach myself more about them, and started using DI Containers.
Main Code (index.php)
$container = new \League\Container\Container();
$container->add("config", function(){
return new Config(APP_ROOT . "/config.json");
});
$container->add("GoogleBooks", GoogleBooksProvider::class)
->withArgument( $container['config'] );
$container->add("books", BookRepository::class);
// empty array, as expected
var_dump($container['books']->getProviders());
// this line doesn't add the provider
$container['books']->addProvider( $container['GoogleBooks'] );
// empty array, should expect to have one entry, GoogleBooksProvider
var_dump($container['books']->getProviders());
BookRepository::addProvider
public function addProvider( iProvider $provider ) {
$this->_providers->push($provider);
return $this;
}
That doesn't work as expected, problem described in the code comments. However, if I swap
$container['books']->addProvider( $container['GoogleBooks'] );
with
$container['books'] = $container['books']->addProvider( $container['GoogleBooks'] );
it works correctly, by storing the GoogleBooksProvider in the BookRepository. Why do I need an assignment operator to make that work correctly?
If I do it without putting it in the container, it works as I expected, without the assignment operator.
$br = new BookRepository();
$br->addProvider( new GoogleBooksProvider($container['config']) );
// shows GoogleBooks is in the _providers array
var_dump($br->getProviders());

Answer 1

Since you are adding, but not sharing the service, you fetch a new instance of BookRepository every time you access the container:
var_dump($container['books'] === $container['books']); // false
If you want to share BookRepository, you need to use this:
$container->add("books", BookRepository::class, true);
or (shorter)
$container->singleton("books", BookRepository::class);