Drupal 8.0.0 beta 12. More info: https://www.drupal.org/node/2514176

core/lib/Drupal/Component/Plugin/LazyPluginCollection.php

@@ -0,0 +1,165 @@
+<?php
+
+/**
+ * @file
+ * Contains \Drupal\Component\Plugin\LazyPluginCollection.
+ */
+
+namespace Drupal\Component\Plugin;
+
+/**
+ * Defines an object which stores multiple plugin instances to lazy load them.
+ *
+ * @ingroup plugin_api
+ */
+abstract class LazyPluginCollection implements \IteratorAggregate, \Countable {
+
+  /**
+   * Stores all instantiated plugins.
+   *
+   * @var array
+   */
+  protected $pluginInstances = array();
+
+  /**
+   * Stores the IDs of all potential plugin instances.
+   *
+   * @var array
+   */
+  protected $instanceIDs = array();
+
+  /**
+   * Initializes and stores a plugin.
+   *
+   * @param string $instance_id
+   *   The ID of the plugin instance to initialize.
+   */
+  abstract protected function initializePlugin($instance_id);
+
+  /**
+   * Gets the current configuration of all plugins in this collection.
+   *
+   * @return array
+   *   An array of up-to-date plugin configuration.
+   */
+  abstract public function getConfiguration();
+
+  /**
+   * Sets the configuration for all plugins in this collection.
+   *
+   * @param array $configuration
+   *   An array of up-to-date plugin configuration.
+   *
+   * @return $this
+   */
+  abstract public function setConfiguration($configuration);
+
+  /**
+   * Clears all instantiated plugins.
+   */
+  public function clear() {
+    $this->pluginInstances = array();
+  }
+
+  /**
+   * Determines if a plugin instance exists.
+   *
+   * @param string $instance_id
+   *   The ID of the plugin instance to check.
+   *
+   * @return bool
+   *   TRUE if the plugin instance exists, FALSE otherwise.
+   */
+  public function has($instance_id) {
+    return isset($this->pluginInstances[$instance_id]) || isset($this->instanceIDs[$instance_id]);
+  }
+
+  /**
+   * Gets a plugin instance, initializing it if necessary.
+   *
+   * @param string $instance_id
+   *   The ID of the plugin instance being retrieved.
+   */
+  public function &get($instance_id) {
+    if (!isset($this->pluginInstances[$instance_id])) {
+      $this->initializePlugin($instance_id);
+    }
+    return $this->pluginInstances[$instance_id];
+  }
+
+  /**
+   * Stores an initialized plugin.
+   *
+   * @param string $instance_id
+   *   The ID of the plugin instance being stored.
+   * @param mixed $value
+   *   An instantiated plugin.
+   */
+  public function set($instance_id, $value) {
+    $this->pluginInstances[$instance_id] = $value;
+    $this->addInstanceId($instance_id);
+  }
+
+  /**
+   * Removes an initialized plugin.
+   *
+   * The plugin can still be used; it will be reinitialized.
+   *
+   * @param string $instance_id
+   *   The ID of the plugin instance to remove.
+   */
+  public function remove($instance_id) {
+    unset($this->pluginInstances[$instance_id]);
+  }
+
+  /**
+   * Adds an instance ID to the available instance IDs.
+   *
+   * @param string $id
+   *   The ID of the plugin instance to add.
+   * @param array|null $configuration
+   *   (optional) The configuration used by this instance. Defaults to NULL.
+   */
+  public function addInstanceId($id, $configuration = NULL) {
+    if (!isset($this->instanceIDs[$id])) {
+      $this->instanceIDs[$id] = $id;
+    }
+  }
+
+  /**
+   * Gets all instance IDs.
+   *
+   * @return array
+   *   An array of all available instance IDs.
+   */
+  public function getInstanceIds() {
+    return $this->instanceIDs;
+  }
+
+  /**
+   * Removes an instance ID.
+   *
+   * @param string $instance_id
+   *   The ID of the plugin instance to remove.
+   */
+  public function removeInstanceId($instance_id) {
+    unset($this->instanceIDs[$instance_id]);
+    $this->remove($instance_id);
+  }
+
+  public function getIterator() {
+    $instances = [];
+    foreach ($this->getInstanceIds() as $instance_id) {
+      $instances[$instance_id] = $this->get($instance_id);
+    }
+    return new \ArrayIterator($instances);
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  public function count() {
+    return count($this->instanceIDs);
+  }
+
+}