Online PHP editor | refs for 3mNJ7

<?php $urls = [ ['url' => 'https://www.example.com/', 'parent_url' => 'https://www.example.com/bleh/bleh.aspx'], ['url' => 'https://www.example2.com/', 'parent_url' => 'https://www.example2.com/blar.aspx'], 'not an array', ['url' => 'https://www.example.com/', 'parent_url' => 'https://www.example.com/bla/bla.aspx'], ]; $urls_uniq = ['https://www.example.com/', 'https://www.example.com/go/173.aspx']; var_export( array_uintersect( $urls, $urls_uniq, function($a, $b) { echo json_encode($a) . ' VS ' . json_encode($b) . "\n"; // return ($a['url'] ?? null) === $b ? 0 : 1; // this doesn't work. // return ($a['url'] ?? $a) === ($b['url'] ?? $b) ? 0 : 1; // this doesn't work return strcmp($a['url'] ?? $a, $b['url'] ?? $b); // or return ($a['url'] ?? $a) <=> ($b['url'] ?? $b); } ) );