Unset::Vars - Perl extension for declaring unset variables
use Unset::Vars;
my $var = unset;
if (is_unset($var)) {
print "var is unset\n";
}
$var = "something";
if (!is_unset($var)) {
print "var is no longer unset\n";
}Sometimes it is useful to know if a variable is not set and not just set to
undef. This module provides a way to declare a variable as unset and to
check if it is unset.
This is also useful in subroutines signatures where you want to know if a variable was passed in or not.
sub attribute ( $self, $var = unset ) {
if ( is_set($var) ) {
$self->{attribute} = $var;
}
else {
return $self->{attribute};
}
}In the above example, we implement the popular (if unfortunate) Perl habit of
using a single method as both a getter an setter. If undef is a valid value
for C<$var>, then you would not be able to distinguish between undef and
not passed in. By using unset you can now tell the difference.
unset, is_unset, and is_set are exported by default.
my $var = unset;Declares a scalar as unset. Sets the scalar to undef.
if (is_unset($var)) {
print "var is unset\n";
} else {
print "var is set\n";
}Returns true if the scalar is unset.
if (is_set($var)) {
print "var is set\n";
} else {
print "var is unset\n";
}Returns true if the variable is set (which might be true even if the variable is undefined).