Changed AbstractPluginManager interface to eliminate need to override constructor in child classes.

module/VuFind/src/VuFind/ServiceManager/AbstractPluginManager.php

@@ -40,8 +40,6 @@ use Zend\ServiceManager\AbstractPluginManager as Base,
  */
 abstract class AbstractPluginManager extends Base
 {
-    protected $expectedInterface;
-
     /**
      * Validate the plugin
      *
@@ -55,11 +53,20 @@ abstract class AbstractPluginManager extends Base
      */
     public function validatePlugin($plugin)
     {
-        if (!($plugin instanceof $this->expectedInterface)) {
+        $expectedInterface = $this->getExpectedInterface();
+        if (!($plugin instanceof $expectedInterface)) {
             throw new ServiceManagerRuntimeException(
                 'Plugin ' . get_class($plugin) . ' does not belong to '
-                . $this->expectedInterface
+                . $expectedInterface
             );
         }
     }
+
+    /**
+     * Return the name of the base class or interface that plug-ins must conform
+     * to.
+     *
+     * @return string
+     */
+    abstract protected function getExpectedInterface();
 }
\ No newline at end of file

module/VuFind/src/VuFind/Session/PluginManager.php

@@ -40,16 +40,13 @@ use Zend\ServiceManager\ConfigInterface;
 class PluginManager extends \VuFind\ServiceManager\AbstractPluginManager
 {
     /**
-     * Constructor
+     * Return the name of the base class or interface that plug-ins must conform
+     * to.
      *
-     * Add a default initializer to ensure the plugin is valid after instance
-     * creation.
-     *
-     * @param null|ConfigInterface $configuration Configuration
+     * @return string
      */
-    public function __construct(ConfigInterface $configuration = null)
+    protected function getExpectedInterface()
     {
-        $this->expectedInterface = 'Zend\Session\SaveHandler\SaveHandlerInterface';
-        parent::__construct($configuration);
+        return 'Zend\Session\SaveHandler\SaveHandlerInterface';
     }
 }
\ No newline at end of file