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wp/wp-content/plugins/woocommerce/includes/rest-api/Utilities/SingletonTrait.php

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+<?php
+/**
+ * Singleton class trait.
+ *
+ * @package WooCommerce\Utilities
+ */
+
+namespace Automattic\WooCommerce\RestApi\Utilities;
+
+/**
+ * Singleton trait.
+ */
+trait SingletonTrait {
+	/**
+	 * The single instance of the class.
+	 *
+	 * @var object
+	 */
+	protected static $instance = null;
+
+	/**
+	 * Constructor
+	 *
+	 * @return void
+	 */
+	protected function __construct() {}
+
+	/**
+	 * Get class instance.
+	 *
+	 * @return object Instance.
+	 */
+	final public static function instance() {
+		if ( null === static::$instance ) {
+			static::$instance = new static();
+		}
+		return static::$instance;
+	}
+
+	/**
+	 * Prevent cloning.
+	 */
+	private function __clone() {}
+
+	/**
+	 * Prevent unserializing.
+	 */
+	final public function __wakeup() {
+		wc_doing_it_wrong( __FUNCTION__, __( 'Unserializing instances of this class is forbidden.', 'woocommerce' ), '4.6' );
+		die();
+	}
+}