design-patterns

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<?php
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namespace App\Creational\Singleton;
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final class Singleton
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{
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    /**
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     * @var null|Singleton
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     */
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    private static ?Singleton $instance = null;
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    /**
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     * Is not allowed to call from outside to prevent from creating multiple instances,
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     * to use the singleton, you have to obtain the instance from Singleton::getInstance() instead.
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     */
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    private function __construct()
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    {
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    }
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    /**
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     * Prevent the instance from being cloned (which would create a second instance of it).
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     */
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    private function __clone()
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    {
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    }
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    /**
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     * Prevent from being unserialized (which would create a second instance of it).
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     */
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    public function __wakeup()
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    {
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        throw new \Exception('Cannot unserialize singleton');
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    }
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    /**
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     * Gets the instance via lazy initialization (created on first usage).
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     *
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     * @return null|Singleton
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     */
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    public static function getInstance(): ?self
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    {
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        if (self::$instance === null) {
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            self::$instance = new self();
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        }
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        return self::$instance;
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    }
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}
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