hash - How can I represent sets in Perl?

Question

I would like to represent a set in Perl. What I usually do is using a hash with some dummy value, e.g.:

my %hash=();
$hash{"element1"}=1;
$hash{"element5"}=1;

Then use if (defined $hash{$element_name}) to decide whether an element is in the set.

Is this a common practice? Any suggestions on improving this?

Also, should I use defined or exists?

Thank you

Answer 1

Yes, building hash sets that way is a common idiom. Note that:

my @keys = qw/a b c d/;
my %hash;
@hash{@keys} = ();

is preferable to using 1 as the value because undef takes up significantly less space. This also forces you to uses exists (which is the right choice anyway).