就像您explode d一样，您可以 implode 再次:

Just like you exploded you can implode again:

$tags = explode(',', $arg);
foreach ($tags as &$tag) {
    $tag = '<a href="' . $u . 'tag/' . $tag . '/" title="' . $tag . '">' . $tag . '</a>';
}

return implode(', ', $tags);