Shortcode for Post Title

/**
 * Post title shortcode.
 * `[post_title]` to use in the loop. Or `[post_title id="123"]` to get a specific post's title, by ID
 * 
 * @return  string  The post's title.
 */
add_shortcode( 'post_title', function( $atts ) {
    $atts = shortcode_atts( array(
        'id' => get_the_ID(),
    ), $atts, 'post_title' );
    return get_the_title( absint( $atts['id'] ) );
});