/ 
Perl-Critic-1.095_001
River stage three • 132 direct dependents • 384 total dependents
/ Perl::Critic::Policy::Variables::ProhibitReusedNames

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.

If you have opinions on this caveat/feature please post to the Perl::Critic mailing list. Perhaps we'll add some specific exemptions?

Performance

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 is not configurable except for the standard options.

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) 2008-2009 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.