WordPress - Get Post Thumbnail URL

get-post-thumbnail.gist.class.php

<?php
   /**
    * Return the Post Thumbnail URL if $post has thumbnail
    * $post is a WordPress Post Object
    * @param $post
    * @return string
    */
   private function getPostThumbnailURL( $post ){

      if ( has_post_thumbnail( $post->ID ) ){

         $img_src = wp_get_attachment_image_src( get_post_thumbnail_id( $post->ID ) );

         return $img_src[0];
      }

      return '';
   }