Laravelium_Feed_validate.php

<?php
$posts = array();
array_push($posts,(object) [
    'title'        => $entry->title
    ,'author'      => $entry->author
    ,'permalink'   => $entry->url
    ,'created'     => new Carbon('2019-07-29 12:24:51')
    ,'description' => $entry->description
    ,'content'     => $entry->content
]);

$feed = App::make('feed');
$feed->setDateFormat('carbon');
$feed->pubdate = $posts[0]->created;

foreach ($posts as $post) {
    $feed->add(
        $post->title
        ,$post->author
        ,$post->permalink
        ,$feed->formatDate($post->created,$feed->getDateFormat()) // Mon, 29 Jul 2019 12:24:51 +0900 と出力される
        ,$post->description
        ,$post->content
    );
}

return $feed->render('rss');