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I've come across the following method signature:
public function register(ServiceProviderInterface $provider, array $values = []){}
I don't understand the part that reads ServiceProviderInterface $provider. Can someone please explain what it does?
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The text before $provider specifies what should the argument be. In this case it should be an instance of ServiceProviderInterface. Read more about type declaration here:
http://php.net/manual/en/functions.arguments.php#functions.arguments.type-declaration