NAME¶
Perl::Critic::Policy::Variables::ProhibitReusedNames - Do not reuse a variable
name in a lexical scope
AFFILIATION¶
This Policy is part of the core Perl::Critic distribution.
DESCRIPTION¶
It's really hard on future maintenance programmers if you reuse a variable name
in a lexical scope. The programmer is at risk of confusing which variable is
which. And, worse, the programmer could accidentally remove the inner
declaration, thus silently changing the meaning of the inner code to use the
outer variable.
my $x = 1;
for my $i (0 .. 10) {
my $x = $i+1; # not OK, "$x" reused
}
With "use warnings" in effect, Perl will warn you if you reuse a
variable name at the same scope level but not within nested scopes. Like so:
% perl -we 'my $x; my $x'
"my" variable $x masks earlier declaration in same scope at -e line 1.
This policy takes that warning to a stricter level.
CAVEATS¶
Crossing subroutines¶
This policy looks across subroutine boundaries. So, the following may be a false
positive for you:
sub make_accessor {
my ($self, $fieldname) = @_;
return sub {
my ($self) = @_; # false positive, $self declared as reused
return $self->{$fieldname};
}
}
This is intentional, though, because it catches bugs like this:
my $debug_mode = 0;
sub set_debug {
my $debug_mode = 1; # accidental redeclaration
}
I've done this myself several times -- it's a strong habit to put that
"my" in front of variables at the start of subroutines.
The current implementation walks the tree over and over. For a big file, this
can be a huge time sink. I'm considering rewriting to search the document just
once for variable declarations and cache the tree walking on that single
analysis.
CONFIGURATION¶
This policy has a single option, "allow", which is a list of names to
never count as duplicates. It defaults to containing $self and $class. You add
to this by adding something like this to your
.perlcriticrc:
[Variables::ProhibitReusedNames]
allow = $self $class @blah
AUTHOR¶
Chris Dolan <cdolan@cpan.org>
This policy is inspired by <
http://use.perl.org/~jdavidb/journal/37548>.
Java does not allow you to reuse variable names declared in outer scopes,
which I think is a nice feature.
COPYRIGHT¶
Copyright (c) 2008-2013 Chris Dolan
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.