WordPress 4.4+ breaks Walker Extension

I upgraded WordPress to 4.5.1 from 4.2.2 and it has broken the functionality I have extending the Walker class. The Walker extension:

class ReturnWalker extends Walker{

public $db_fields = array( 'parent' => 'parent', 
                           'id' => 'term_id' );
public $show_all = FALSE;       

/*
*
*   @param array
*   @param object
*   @param int
*   @param
*   @return NULL
*/
public function start_el( &$output, $category, $depth = 0, $args = array(), $current_object_id = 0) {
    if( !is_array($output) )
        $output = array();

    $id = $this->db_fields['id'];
    $parent = $this->db_fields['parent'];

    if( $depth == 0 || (!$category->$parent) ){
        $output[$category->term_id] = $category;
    } else if( $depth > 0){
        $this->search( $output, $category->$parent, $category );
    }
}

/*
*
*   @param array
*   @param int 
*   @param object
*/
private function search( &$output, $key, $category){

    $id = $this->db_fields['id'];
    $parent = $this->db_fields['parent'];


    if( count($output) ){
        foreach( $output as $k => &$object){
            if( $k == $key ){
                $object->children[$category->term_id] = $category;
                return;
            } else if( isset($object->children[$key]) ){
                $this->search( $object->children, $category->$parent, $category );
            }
        }
    } else if( $this->show_all){
        $output[$category->$id] = $category;
    }
}

/*
*   sets the field names used for id and parent id
*   @param array(
*               'id' => string
*               'parent' => string
*          )
*   @return NULL
*/
public function setDbFields( array $db_fields){
    $this->db_fields = array_merge( $this->db_fields, $db_fields );
}
}

takes categories retrieved by using “get_the_terms()” and passes it in to the walk method:

$breadcrumbs = new ReturnWalker;
$category = get_the_terms( $post->ID, 'category' );
$struct = $breadcrumbs->walk( $category, 0 );

After some careful observation I noticed that $category is now an array of WP_Term objects and that the WP_Term class is final. This breaks the extension because it depended on the ability to add the property “children”, but because the class is non-mutable, is no longer possible.

The end product is that the functionality would build out URLs and breadcrumbs based off of the custom taxonomy which the post lived under. Does anyone have any good solutions to this type of issue?

Update –
Creating a class that mimics WP_Terms and copying over the objects returned by get_the_terms() to my *_Terms class worked. Passing in the returned objects when instantiating my class hits the constructor and builds out a copy of the properties that I have control over without worrying about core code changes:

                $categoryTerms = get_the_terms( $post->ID, 'category' );

                foreach( $categoryTerms as $categoryTerm ){
                    $category[] = new MyTerm( $categoryTerm );
                }

                $breadcrumbs = new MyWalker;
                $struct = $breadcrumbs->walk( $category, 0, array());

Your original solution was a hack, and no surprise it failed. In general never add methods/attributes to objects that you do not control their class and future development.

The right way is to create your own object to be passed to the walker. Pass to it the category object on construction and either populate fields is a similar way to the category object or write accesor functions for it (for full hacking points use _get() and _set() 😉 ). Design it good enough and your walker code will not have to change at all, only the initialization.