protected function cacheAddByRef(string $primary_key, $ref_key, &$value)
    {
        $ref_key                                               = (string) $ref_key;
        $this->x___cache['x___refs'][$primary_key][$ref_key][] = &$value;
    }
protected function cacheAddByRef(string $primary_key, $ref_key, &$value)
    {
        $ref_key                                               = (string) $ref_key;
        $this->x___cache['x___refs'][$primary_key][$ref_key][] = &$value;
    }
protected function cacheAddByRef ( string $ primary_key , $ ref_key , & $ value ) { $ ref_key = ( string ) $ ref_key ; $ this -> x___cache [ 'x___refs' ] [ $ primary_key ] [ $ ref_key ] [ ] = & $ value ; }
Add a new cache ref-key.

@since 150424 Initial release.

@param string     $primary_key Primary key.
@param string|int $ref_key     Ref-key to set.
@param mixed      $value       New value (by reference).
Add a new cache ref - key .