Perl::Critic::Policy:Perl::Critic::Policy::Subroutines::RequireArgUnpacking(3)NAMEPerl::Critic::Policy::Subroutines::RequireArgUnpacking - Always unpack
"@_" first.
AFFILIATION
This Policy is part of the core Perl::Critic distribution.
DESCRIPTION
Subroutines that use @_ directly instead of unpacking the arguments to
local variables first have two major problems. First, they are very
hard to read. If you're going to refer to your variables by number
instead of by name, you may as well be writing assembler code! Second,
@_ contains aliases to the original variables! If you modify the
contents of a @_ entry, then you are modifying the variable outside of
your subroutine. For example:
sub print_local_var_plus_one {
my ($var) = @_;
print ++$var;
}
sub print_var_plus_one {
print ++$_[0];
}
my $x = 2;
print_local_var_plus_one($x); # prints "3", $x is still 2
print_var_plus_one($x); # prints "3", $x is now 3 !
print $x; # prints "3"
This is spooky action-at-a-distance and is very hard to debug if it's
not intentional and well-documented (like "chop" or "chomp").
An exception is made for the usual delegation idiom
"$object->SUPER::something( @_ )". Only "SUPER::" and "NEXT::" are
recognized (though this is configurable) and the argument list for the
delegate must consist only of "( @_ )".
CONFIGURATION
This policy is lenient for subroutines which have "N" or fewer top-
level statements, where "N" defaults to ZERO. You can override this to
set it to a higher number with the "short_subroutine_statements"
setting. This is very much not recommended but perhaps you REALLY need
high performance. To do this, put entries in a .perlcriticrc file like
this:
[Subroutines::RequireArgUnpacking]
short_subroutine_statements = 2
By default this policy does not allow you to specify array subscripts
when you unpack arguments (i.e. by an array slice or by referencing
individual elements). Should you wish to permit this, you can do so
using the "allow_subscripts" setting. This defaults to false. You can
set it true like this:
[Subroutines::RequireArgUnpacking]
allow_subscripts = 1
The delegation logic can be configured to allow delegation other than
to "SUPER::" or "NEXT::". The configuration item is
"allow_delegation_to", and it takes a space-delimited list of allowed
delegates. If a given delegate ends in a double colon, anything in the
given namespace is allowed. If it does not, only that subroutine is
allowed. For example, to allow "next::method" from "Class::C3" and
_delegate from the current namespace in addition to SUPER and NEXT, the
following configuration could be used:
[Subroutines::RequireArgUnpacking]
allow_delegation_to = next::method _delegate
CAVEATS
PPI doesn't currently detect anonymous subroutines, so we don't check
those. This should just work when PPI gains that feature.
We don't check for @ARG, the alias for @_ from English.pm. That's
deprecated anyway.
CREDITS
Initial development of this policy was supported by a grant from the
Perl Foundation.
AUTHOR
Chris Dolan <cdolan@cpan.org>
COPYRIGHT
Copyright (c) 2007-2011 Chris Dolan. Many 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 v5.14.1Perl::Critic::Policy::Subroutines::RequireArgUnpacking(3)
