my %seen;
for my $i (reverse (0 .. @$ref-1)) {
    # replaces current item in array with last item
    # and removes the last element if id already seen
    $ref->[$i] = pop @$ref if $seen{$ref->[$i]->{id}}++;
}

##</code><code>##

my %seen;
my $removed = 0;
for my $i (0 .. @$ref-1) {
    my $item = $ref->[$i];
    $seen{$item->{id}}++ ? $removed++ : ($ref->[$i-$removed] = $item);
}
splice @$ref,-$removed;