Perl::Critic::Policy::ControlStructures::ProhibitPostfixControls(3)
NAME
Perl::Critic::Policy::ControlStructures::ProhibitPostfixControls -
Write "if($condition){ do_something() }" instead of "do_something() if
$condition".
AFFILIATION
This Policy is part of the core Perl::Critic distribution.
DESCRIPTION
Conway discourages using postfix control structures ("if", "for",
"unless", "until", "when", "while") because they hide control flow.
The "unless" and "until" controls are particularly evil because they
lead to double-negatives that are hard to comprehend. The only
tolerable usage of a postfix "if"/"when" is when it follows a loop
break such as "last", "next", "redo", or "continue".
do_something() if $condition; # not ok
if ($condition) { do_something() } # ok
do_something() while $condition; # not ok
while ($condition) { do_something() } # ok
do_something() unless $condition; # not ok
do_something() unless ! $condition; # really bad
if (! $condition) { do_something() } # ok
do_something() until $condition; # not ok
do_something() until ! $condition; # really bad
while (! $condition) { do_something() } # ok
do_something($_) for @list; # not ok
LOOP:
for my $n (0..100) {
next if $condition; # ok
last LOOP if $other_condition; # also ok
next when m< 0 \z >xms; # fine too
}
CONFIGURATION
A set of constructs to be ignored by this policy can specified by
giving a value for 'allow' of a string of space-delimited keywords:
"if", "for", "unless", "until", "when", and/or "while". An example of
specifying allowed flow-control structures in a .perlcriticrc file:
[ControlStructures::ProhibitPostfixControls]
allow = for if until
By default, all postfix control keywords are prohibited.
The set of flow-control functions that are exempt from the restriction
can also be configured with the 'flowcontrol' directive in your
.perlcriticrc file:
[ControlStructures::ProhibitPostfixControls]
flowcontrol = warn die carp croak cluck confess goto exit
This is useful if you're using additional modules that add things like
"assert" or "throw".
NOTES
The "die", "croak", and "confess" functions are frequently used as
flow-controls just like "next" or "last". So this Policy does permit
you to use a postfix "if" when the statement begins with one of those
functions. It is also pretty common to use "warn", "carp", and "cluck"
with a postfix "if", so those are allowed too.
The "when" keyword was added to the language after Perl Best Practices
was written. This policy treats "when" the same way it does "if", i.e.
it's allowed after flow-control constructs. Thanks to brian d foy for
the inspiration <http://www.effectiveperlprogramming.com/blog/543>.
BUGS
Look for the "do {} while" case and change the explanation to point to
page 123 when it is found. RT #37905.
AUTHOR
Jeffrey Ryan Thalhammer <jeff@imaginative-software.com>
COPYRIGHT
Copyright (c) 2005-2011 Imaginative Software Systems. All rights
reserved.
This program is free software; you can redistribute it and/or modify it
under the same terms as Perl itself. The full text of this license can
be found in the LICENSE file included with this module.
perl v5.28.Perl::Critic::Policy::ControlStructures::ProhibitPostfixControls(3)
perl-critic 1.134.0 - Generated Mon Jun 3 10:56:44 CDT 2019