public function dirs(?int $constraints = null): \Generator
    {
        foreach ($this->all($constraints) as $directory) {
            if ($directory->isDir()) {
                yield $directory;
            }
        }
    }
public function dirs(?int $constraints = null): \Generator
    {
        foreach ($this->all($constraints) as $directory) {
            if ($directory->isDir()) {
                yield $directory;
            }
        }
    }
public function dirs ( ? int $ constraints = null ) : \ Generator { foreach ( $ this -> all ( $ constraints ) as $ directory ) { if ( $ directory -> isDir ( ) ) { yield $ directory ; } } }
list only directories
@param int|null $constraints
@return Directory[]
list only directories