Perl Best Practices [Electronic resources]

3.2. Booleans

Name booleans after their associated test .

A special case can be made for subroutines that return boolean values, and for variables that store them. These should be named for the properties or predicates they test, in such a way that the resulting conditional expressions read naturally. Often that rule will mean they begin with is_ or has_, but not always. For example:

sub is_valid;
sub metadata_available_for;
sub has_end_tag;
my $loading_finished;
my $has_found_bad_record;
# and later...
if (is_valid($next_record) && !$loading_finished) {
METADATA:
while (metadata_available_for($next_record)) {
push @metadata, get_metadata_for($next_record);
last METADATA if has_end_tag($next_record);
}
}
else {
$has_found_bad_record = 1;
} 

Again, explicit and longer names are strongly preferred. Compare the readability of the previous code with the following:

sub ok;
sub metadata;
sub end_tag;
my $done;
my $bad;
# and later...
if (ok($next_record) && !$done) {               # Ok in what sense? What is done?
METADATA:
while (metadata($next_record)) {            # Metadata exists? Defined? True?
push @metadata, get_metadata_for($next_record);
last METADATA if end_tag($next_record); # Does this set an end tag?
}
}
else {
$bad = 1;                                   # What's bad? In what way?
}