SandwichPluginManager.php

<?php

namespace Drupal\plugin_type_example;

use Drupal\Core\Cache\CacheBackendInterface;
use Drupal\Core\Extension\ModuleHandlerInterface;
use Drupal\Core\Plugin\DefaultPluginManager;
use Drupal\plugin_type_example\Annotation\Sandwich;

/**
 * A plugin manager for sandwich plugins.
 *
 * The SandwichPluginManager class extends the DefaultPluginManager to provide
 * a way to manage sandwich plugins. A plugin manager defines a new plugin type
 * and how instances of any plugin of that type will be discovered, instantiated
 * and more.
 *
 * Using the DefaultPluginManager as a starting point sets up our sandwich
 * plugin type to use annotated discovery.
 *
 * The plugin manager is also declared as a service in
 * plugin_type_example.services.yml so that it can be easily accessed and used
 * anytime we need to work with sandwich plugins.
 */
class SandwichPluginManager extends DefaultPluginManager {
    
    /**
     * Creates the discovery object.
     *
     * @param \Traversable $namespaces
     *   An object that implements \Traversable which contains the root paths
     *   keyed by the corresponding namespace to look for plugin implementations.
     * @param \Drupal\Core\Cache\CacheBackendInterface $cache_backend
     *   Cache backend instance to use.
     * @param \Drupal\Core\Extension\ModuleHandlerInterface $module_handler
     *   The module handler to invoke the alter hook with.
     */
    public function __construct(\Traversable $namespaces, CacheBackendInterface $cache_backend, ModuleHandlerInterface $module_handler) {
        // We replace the $subdir parameter with our own value.
        // This tells the plugin manager to look for Sandwich plugins in the
        // 'src/Plugin/Sandwich' subdirectory of any enabled modules. This also
        // serves to define the PSR-4 subnamespace in which sandwich plugins will
        // live. Modules can put a plugin class in their own namespace such as
        // Drupal\{module_name}\Plugin\Sandwich\MySandwichPlugin.
        $subdir = 'Plugin/Sandwich';
        // The name of the interface that plugins should adhere to. Drupal will
        // enforce this as a requirement. If a plugin does not implement this
        // interface, Drupal will throw an error.
        $plugin_interface = SandwichInterface::class;
        // The name of the annotation class that contains the plugin definition.
        $plugin_definition_annotation_name = Sandwich::class;
        parent::__construct($subdir, $namespaces, $module_handler, $plugin_interface, $plugin_definition_annotation_name);
        // This allows the plugin definitions to be altered by an alter hook. The
        // parameter defines the name of the hook, thus: hook_sandwich_info_alter().
        // In this example, we implement this hook to change the plugin definitions:
        // see plugin_type_example_sandwich_info_alter().
        $this->alterInfo('sandwich_info');
        // This sets the caching method for our plugin definitions. Plugin
        // definitions are discovered by examining the $subdir defined above, for
        // any classes with an $plugin_definition_annotation_name. The annotations
        // are read, and then the resulting data is cached using the provided cache
        // backend. For our Sandwich plugin type, we've specified the @cache.default
        // service be used in the plugin_type_example.services.yml file. The second
        // argument is a cache key prefix. Out of the box Drupal with the default
        // cache backend setup will store our plugin definition in the cache_default
        // table using the sandwich_info key. All that is implementation details
        // however, all we care about it that caching for our plugin definition is
        // taken care of by this call.
        $this->setCacheBackend($cache_backend, 'sandwich_info', [
            'sandwich_info',
        ]);
    }

}