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<?php declare(strict_types=1); |
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namespace League\Container\ServiceProvider; |
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use Generator; |
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use League\Container\{ContainerAwareInterface, ContainerAwareTrait}; |
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use League\Container\Exception\ContainerException; |
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class ServiceProviderAggregate implements ServiceProviderAggregateInterface |
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{ |
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use ContainerAwareTrait; |
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/** |
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* @var \League\Container\ServiceProvider\ServiceProviderInterface[] |
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*/ |
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protected $providers = []; |
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/** |
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* @var array |
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*/ |
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protected $registered = []; |
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/** |
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* {@inheritdoc} |
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*/ |
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public function add($provider): ServiceProviderAggregateInterface |
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{ |
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if (is_string($provider) && $this->getContainer()->has($provider)) { |
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$provider = $this->getContainer()->get($provider); |
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} elseif (is_string($provider) && class_exists($provider)) { |
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$provider = new $provider; |
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} |
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if ($provider instanceof ContainerAwareInterface) { |
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$provider->setContainer($this->getContainer()); |
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} |
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if ($provider instanceof BootableServiceProviderInterface) { |
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$provider->boot(); |
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} |
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if ($provider instanceof ServiceProviderInterface) { |
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$this->providers[] = $provider; |
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return $this; |
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} |
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throw new ContainerException( |
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'A service provider must be a fully qualified class name or instance ' . |
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'of (\League\Container\ServiceProvider\ServiceProviderInterface)' |
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); |
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} |
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/** |
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* {@inheritdoc} |
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*/ |
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public function provides(string $service): bool |
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{ |
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foreach ($this->getIterator() as $provider) { |
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if ($provider->provides($service)) { |
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return true; |
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} |
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} |
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return false; |
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} |
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/** |
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* {@inheritdoc} |
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*/ |
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public function getIterator(): Generator |
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{ |
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$count = count($this->providers); |
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for ($i = 0; $i < $count; $i++) { |
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yield $this->providers[$i]; |
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} |
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} |
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/** |
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* {@inheritdoc} |
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*/ |
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public function register(string $service) |
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{ |
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if (! $this->provides($service)) { |
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throw new ContainerException( |
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sprintf('(%s) is not provided by a service provider', $service) |
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); |
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} |
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foreach ($this->getIterator() as $provider) { |
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if (in_array($provider->getSignature(), $this->registered)) { |
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return; |
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} |
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$provider->register(); |
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$this->registered[] = $provider->getSignature(); |
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} |
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} |
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} |
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If you return a value from a function or method, it should be a sub-type of the type that is given by the parent type f.e. an interface, or abstract method. This is more formally defined by the Lizkov substitution principle, and guarantees that classes that depend on the parent type can use any instance of a child type interchangably. This principle also belongs to the SOLID principles for object oriented design.
Let’s take a look at an example:
Our function
my_function
expects aPost
object, and outputs the author of the post. The base classPost
returns a simple string and outputting a simple string will work just fine. However, the child classBlogPost
which is a sub-type ofPost
instead decided to return anobject
, and is therefore violating the SOLID principles. If aBlogPost
were passed tomy_function
, PHP would not complain, but ultimately fail when executing thestrtoupper
call in its body.