/ 
Perl-Critic-Policy-ValuesAndExpressions-ProhibitDefinedBeforeLength-0.001
/ Perl::Critic::Policy::ValuesAndExpressions::ProhibitDefinedBeforeLength

NAME

Perl::Critic::Policy::ValuesAndExpressions::ProhibitDefinedBeforeLength - Test the value, not its length, and shape it before measuring it.

VERSION

version 0.001

Perl::Critic::Policy::ValuesAndExpressions::ProhibitDefinedBeforeLength

Asking whether a value is defined and then whether it has a length is two operations where one does the job, and in a boolean context neither is needed:

return unless defined $uri && length $uri;      # what you see - violates
return unless length $uri;                      # what it means - still violates
return unless $uri;                             # what should actually be done

When the length itself matters, shape the value before the comparison rather than guarding the comparison:

return if defined $uri && length $uri > 2048;   # we care about the length - violates
$uri //= q{};                                   # shape the data first
return if length $uri > 2048;                   # correct solution

Under use warnings FATAL => 'all', length(undef) > 2048 dies. That is working as designed: you should validate/coerce your inputs type before you start blithely shoving them into conditionals past which they subtly pollute your program.

In a boolean context, the value alone is false for undef, the empty string and "0". length is true for "0", and that difference is the reason the pattern spread. It catches as many bugs as it causes:

my $a = read_value_from_file(...);
my $b = read_value_from_file(...);    # guess what read() returns? not integers!
if (length($a)) { print $a }          # hey this is great, maybe saved a print op.
if (length($b)) { return 5 / $b }     # Now I've got a divide by zero bug.

so the policy asks for the cheaper test, since there is no avoiding awareness of this distinction in perl.

Where "0" is a value you actually want the length of, say so with a ## no critic and a reason.

The saving is largest in a loop, where the redundant ops run per element:

grep { defined $_ && length $_ } @list;         # 3 calls
grep { length } @list;                          # one call
grep { $_ } @list;                              # no calls!

PROHIBITED

Anywhere:

defined $x && length $x
defined($x) and length($x)
defined $h->{key} && length $h->{key}
defined && length                               # both of $_
defined $x && length $x > 3                     # shape $x first

!defined $x || !length $x                       # the negation
not defined $x or not length $x

In a boolean context -- the condition of if, unless, while or until, a statement modifier, the operand of ! or not, the condition of ?:, or the block of grep, first, any, all, none or notall:

length $x                                       # waste of time in boolean context
!length $x

ALLOWED

$x                                              # in a boolean context
defined $x && length $y                         # two different values
defined $x && $x ne q{}
length $x > 3                                   # the length is used
my $size = length $x;                           # not a boolean context

defined $x && $x ne q{} is a different way to write the test, and is not reported.

CAVEATS

Assigning the result of length and using it later will not be checked.

A length that is the operand of && or || in an assignment or a return, such as return length $x && $y, is a value rather than a condition, and is not reported either.

CONFIGURATION

None.

METHODS

What Perl::Critic::Policy asks of a policy, answered here rather than called from anywhere.

supported_parameters

None.

BUGS

Please report any bugs or feature requests on the bugtracker website https://github.com/teodesian/perl-critic-policy-prohibitdefinedbeforelength/issues

When submitting a bug or request, please include a test-file or a patch to an existing test-file that illustrates the bug or desired feature.

AUTHORS

Current Maintainers:

  • George S. Baugh <george@troglodyne.net>

COPYRIGHT AND LICENSE

Copyright (c) 2026 Troglodyne LLC

Permission is hereby granted, free of charge, to any person obtaining a copy of this software and associated documentation files (the "Software"), to deal in the Software without restriction, including without limitation the rights to use, copy, modify, merge, publish, distribute, sublicense, and/or sell copies of the Software, and to permit persons to whom the Software is furnished to do so, subject to the following conditions: The above copyright notice and this permission notice shall be included in all copies or substantial portions of the Software. THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.