my @array = ();
push (@array, $rel_path);
## in my code more than one thing is pushed to @array.
push (@{$self->{files}}, \@array);

##</code><code>##

sub next {
    my( $self )= @_;

    while( 1 ) {
        if(  @{ $self->{files} }  ) {
            my $file = shift @{ $self->{files} };   ## HERE!
            if(  -d $file  ) {
                push @{ $self->{dirs} }, $file;
            }
            return $file;
        }
        if(  ! @{ $self->{dirs} }  ) {
            return;
        }
        my $dir= shift @{ $self->{dirs} };
        if(  opendir( DIR, $dir )  ) {
            $self->{files}= [
                map {
                    File::Spec->catfile( $dir, $_ );
                } File::Spec->no_upwards( readdir(DIR) )
            ];
            closedir DIR;
        } else {
            warn "opendir failed, $dir: $!\n";
        }
    }
}

##</code><code>##

my $file;
while(  $file = $f->next()  ) {
	print "@{$_}\n";
}

##</code><code>##

push (@{$self->{output}}, [$rel_path, $var1, $var2]);