Perl::Critic::Policy::ControlStructures::ProhibitPostfixControls - Write C<if if $condition>. |
Perl::Critic::Policy::ControlStructures::ProhibitPostfixControls - Write if($condition){ do_something() }
instead of 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
.
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
.
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.
Look for the do {} while
case and change the explanation to point
to page 123 when it is found. RT #37905.
Jeffrey Ryan Thalhammer <jeff@imaginative-software.com>
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::Critic::Policy::ControlStructures::ProhibitPostfixControls - Write C<if if $condition>. |