Perl::Critic::Policy::ControlStructures::ProhibitPostfixControls - Write if($condition){ do_something() } instead of do_something() if $condition.
if($condition){ do_something() }
do_something() if $condition
This Policy is part of the core Perl::Critic distribution.
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.
if
for
unless
until
when
while
last
next
redo
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 }
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.
assert
throw
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.
die
croak
confess
warn
carp
cluck
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.
Look for the do {} while case and change the explanation to point to page 123 when it is found. RT #37905.
do {} while
Jeffrey Ryan Thalhammer <jeff@imaginative-software.com>
Copyright (c) 2005-2011 Imaginative Software Systems. All rights reserved.
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