for my $i ( 0 .. $#{ $self->{ keys } } ) {
	my $id = $self->{ keys }->[ $i ];
	# ...
}

##</code><code>##

for my $i ( 0 .. $self->max_index() ) {
	my ( $key, $value ) = $self->at( $i );
	# ...
}

##</code><code>##

my $iter = $self->iterator();

while( my ( $key, $value ) = $iter->() ) {
	# ...
}