Consider this example:

#!/usr/bin/env perl

my $vec0;

# set the first bit of vec0 to false
vec($vec0, 0, 1) = 0;

print "vec0 is " . length($vec0) . " bytes longn";

if ($vec0) {
  # what
  print "vec0 is True!n";
}

A vec used in evaluation seems to (almost) always be True – this is because a vec is really a string, and so $vec0 is a string containing “” which is not False according to Perl: only strings “” and “0” are False.

(aside: this is False, despite being non-zero:

vec($vec0, 5, 1) = 1;
vec($vec0, 4, 1) = 1;

because 0x30 is the ASCII code for 0)

Fine: what is the “correct” way to check for an “empty” vector? Count bits with unpack, regex test m/^*$/, “normalize” all vectors by chopping empty bytes off the end? This seems like it should be a solved problem… and why does Perl not treat vec magically for true/false?