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lib/pkp/classes/core/maps/Base.php

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+<?php
+/**
+ * @file classes/core/maps/Base.php
+ *
+ * Copyright (c) 2014-2020 Simon Fraser University
+ * Copyright (c) 2000-2020 John Willinsky
+ * Distributed under the GNU GPL v3. For full terms see the file docs/COPYING.
+ *
+ * @class Base
+ *
+ * @brief A base class for creating extensible maps of any kind.
+ */
+
+namespace PKP\core\maps;
+
+abstract class Base
+{
+    /** @var array Callbacks that should be applied to each object in the map. */
+    protected $extensions = [];
+
+    /**
+     * Extend the map with a custom callback function
+     *
+     * Example:
+     *
+     * $map->extend(function($output, $input, $map) {
+     *   $output['example'] = $input->example;
+     *   return $output;
+     * })
+     *
+     */
+    public function extend(callable $cb): self
+    {
+        $this->extensions[] = $cb;
+        return $this;
+    }
+
+    /**
+     * Run extensions applied to this map
+     *
+     * Run the callback functions registered with extend.
+     *
+     * @param mixed $output The output the object is being mapped to
+     * @param mixed $input The object that is being mapped from
+     */
+    protected function withExtensions($output, $input)
+    {
+        foreach ($this->extensions as $extension) {
+            $output = call_user_func($extension, $output, $input, $this);
+        }
+        return $output;
+    }
+}