private function buildLevelsString($levels)
    {
        $this->levelsString = join(DIRECTORY_SEPARATOR, array_fill(0, $levels, '%s')) . DIRECTORY_SEPARATOR;

        return $this;
    }
private function buildLevelsString($levels)
    {
        $this->levelsString = join(DIRECTORY_SEPARATOR, array_fill(0, $levels, '%s')) . DIRECTORY_SEPARATOR;

        return $this;
    }
private function buildLevelsString ( $ levels ) { $ this -> levelsString = join ( DIRECTORY_SEPARATOR , array_fill ( 0 , $ levels , '%s' ) ) . DIRECTORY_SEPARATOR ; return $ this ; }
Builds a string with placeholders and directory separators required to
create a path for saving a final cache entry.

For example if $levels = 3 and DIRECTORY_SEPARATOR = '/':
%s/%s/%s/

@param int $levels
@return $this
Builds a string with placeholders and directory separators required to create a path for saving a final cache entry .