Your code could be condensed to

my @set = qw(a a b c c);
my %seen;
my @unique = grep { not $seen{$_} ++ } @set;
[download]

That method preserves the order of the original array but if that's not important you could also do

my @set = qw(a a b c c);
my %seen;
@seen{@set} = ();
my @unique = keys %seen;
[download]

I hope this is of interest.

Cheers,

JohnGG