diff --git a/src/Util/Functional.php b/src/Util/Functional.php
new file mode 100644
index 0000000000..eb5297663e
--- /dev/null
+++ b/src/Util/Functional.php
@@ -0,0 +1,67 @@
+<?php
+
+declare(strict_types = 1);
+
+// {{{ License
+// This file is part of GNU social - https://www.gnu.org/software/social
+//
+// GNU social is free software: you can redistribute it and/or modify
+// it under the terms of the GNU Affero General Public License as published by
+// the Free Software Foundation, either version 3 of the License, or
+// (at your option) any later version.
+//
+// GNU social is distributed in the hope that it will be useful,
+// but WITHOUT ANY WARRANTY; without even the implied warranty of
+// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+// GNU Affero General Public License for more details.
+//
+// You should have received a copy of the GNU Affero General Public License
+// along with GNU social.  If not, see <http://www.gnu.org/licenses/>.
+// }}}
+
+/**
+ * String formatting utilities
+ *
+ * @package   GNUsocial
+ * @category  Util
+ *
+ * @author    Hugo Sales <hugo@hsal.es>
+ * @copyright 2020-2021 Free Software Foundation, Inc http://www.fsf.org
+ * @license   https://www.gnu.org/licenses/agpl.html GNU AGPL v3 or later
+ */
+
+namespace App\Util;
+
+abstract class Functional
+{
+    /**
+     * TODO replace with \Functional\cartesian_product when it gets merged upstream
+     */
+    public static function cartesianProduct(string|array $separator, ...$collections)
+    {
+        $aggregation = [];
+        $left        = array_shift($collections);
+        while (true) {
+            $right = array_shift($collections);
+            foreach ($left as $l) {
+                foreach ($right as $r) {
+                    if (\is_string($separator)) {
+                        $aggregation[] = "{$l}{$separator}{$r}";
+                    } elseif (\is_array($separator)) {
+                        foreach ($separator as $sep) {
+                            $aggregation[] = "{$l}{$sep}{$r}";
+                        }
+                    }
+                }
+            }
+            if (empty($collections)) {
+                break;
+            } else {
+                $left        = $aggregation;
+                $aggregation = [];
+            }
+        }
+
+        return $aggregation;
+    }
+}