class-wp-doc-collection.php

<?php
/**
 * WP Docs Collection Class
 *
 * Stores commonly
 *
 * @access public
 * @since 3.7.0
 */

class WP_Docs_Collection {

	/**
	 * Post Columns
	 *
	 * @access public
	 * @since 3.7.0
	 */
	private static $post_columns = array(
		'ID', 'post_author', 'post_date', 'post_date_gmt',
		'post_content', 'post_title', 'post_excerpt',
		'post_status', 'comment_status', 'ping_status',
		'post_password', 'post_name', 'to_ping', 'pinged',
		'post_modified', 'post_modified_gmt',
		'post_content_filtered', 'post_parent', 'guid',
		'menu_order', 'post_type', 'post_mime_type','comment_count'
	);

	public static get_post_columns(){
		return self::$post_columns;
	}

}

post-columns.php

<?php

function get_post_columns(){
    static $columns = null;
    if(!$columns){
        $columns = array(
            'ID', 'post_author', 'post_date', 'post_date_gmt',
            'post_content', 'post_title', 'post_excerpt',
            'post_status', 'comment_status', 'ping_status',
            'post_password', 'post_name', 'to_ping', 'pinged',
            'post_modified', 'post_modified_gmt',
            'post_content_filtered', 'post_parent', 'guid',
            'menu_order', 'post_type', 'post_mime_type','comment_count'
        );
    }
    return $columns;
}