Loop – how to get previous/next post for first/last post?

I have a simple loop for a JS slider, I want to display previous and next posts titles on my slide, but I can’t get previous post title on the first slide (because apparently first post have no previous posts):

$prev_post = $loop->posts[$loop->current_post - 1]; // ALWAYS NULL FOR FIRST POST :(
$next_post = $loop->posts[$loop->current_post + 1]; // ALWAYS NULL FOR THE LAST POST
echo $next_post->post_title;
echo $next_post->post_title; 

Is there any easy way to fix that?

You can loop the slides quite simply:

$prev_index = ( $loop->current_post == 0 ) ? count( $loop->posts ) - 1 : $loop->current_post - 1;
$next_index = ( $loop->current_post == count( $loop->posts ) - 1 ) ? 0 : $loop->current_post + 1;

$prev_post = $loop->posts[ $prev_index ];
$next_post = $loop->posts[ $next_index ];

echo $next_post->post_title;
echo $next_post->post_title;

This takes the last post for the previous post if the current post is the first post, and the first post for the next post if the current post is the last post.