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<?php |
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namespace Gandung\Promise; |
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/** |
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* @author Paulus Gandung Prakosa <[email protected]> |
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*/ |
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class FulfilledPromise implements PromiseInterface |
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{ |
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/** |
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* @var mixed |
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*/ |
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private $value; |
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public function __construct($value) |
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{ |
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if (method_exists($value, 'then')) { |
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throw new \InvalidArgumentException( |
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sprintf("Unable to get instance of %s with promise as constructor parameter.", __CLASS__) |
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); |
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} |
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$this->value = $value; |
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} |
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/** |
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* {@inheritdoc} |
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*/ |
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public function then($onFulfilled = null, $onRejected = null) |
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{ |
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if (!$onFulfilled) { |
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return $this; |
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} |
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$q = new Promise(); |
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$value = $this->value; |
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Context\ContextStack::create()->store(static function () use ($q, $value, $onFulfilled) { |
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if ($q->currentState() === self::STATE_PENDING) { |
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try { |
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$q->resolve($onFulfilled($value)); |
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} catch (\Throwable $e) { |
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$q->reject($e); |
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} catch (\Exception $e) { |
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$q->reject($e); |
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} |
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} |
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}); |
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Context\ContextStack::getQueueHandler()->run(); |
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return $q; |
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} |
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/** |
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* Resolving the promise if given value are equal to current value. Otherwise, |
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* throws an exception. |
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* |
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* @param integer $value |
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* @throws \Exception |
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*/ |
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public function resolve($value) |
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{ |
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if ($value !== $this->value) { |
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throw new \LogicException( |
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sprintf( |
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"Supplied value does not strictly equal to current value." . |
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"Cannot resolve promise from context '%s'", __CLASS__ |
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) |
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); |
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} |
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} |
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/** |
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* Rejecting this promise will throw an exception because the state of current |
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* promise is fulfilled. |
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* |
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* @param mixed $reason |
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* @throws \Exception |
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*/ |
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public function reject($reason) |
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{ |
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throw new \LogicException( |
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sprintf( |
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"Cannot rejected a promise from context '%s'", __CLASS__ |
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) |
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); |
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} |
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/** |
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* Return the state of current promise. |
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* |
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* @return integer |
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*/ |
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public function currentState() |
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{ |
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return self::STATE_FULFILLED; |
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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.