Perl::Critic::Policy::ValuesAndExpressions::ProhibitDuplicateHashKeys(3pm)

Overview

This policy is part of the "Perl::Critic::Pulp" add-on. It reports duplicate literal hash keys in a hash assignment or anonymous hashref.

    my %hash = (red   => 1,
                green => 2,
                red   => 3,    # bad
               );
    my $hashref = { red   => 1,
                    red   => 3,   # bad
                  };

Writing duplicate literal keys is probably a mistake or too much cut and paste, and if the values are different will make it unclear to human readers what was meant. On that basis this policy is under the "bugs" theme and medium severity (see "POLICY THEMES" in Perl::Critic).

Perl is happy to run code like the above. The value of the last "red" is stored. As runtime behaviour, this is good since you can give defaults which further values from a caller or similar can replace. For example,

    sub new {
      my $class = shift;
      return bless { foo => 'default',
                     bar => 'default',
                     @_ }, $class;
    }
    MyClass->new (foo => 'caller value'); # overriding 'default'

Expressions

Expressions within a hash list cannot be checked in general. Some concatenations of literals are recognised though they're probably unusual.

    my %hash = (ab      => 1,
                'a'.'b' => 2);  # bad
    my %hash = (__PACKAGE__.'a' => 1,
                __PACKAGE__.'a' => 2);  # bad

Function calls etc within a list might return an odd or even number of values. Fat commas "=>" are taken as indicating a key when in doubt.

    my %hash = (blah()    => 1,  # guided by =>
                a         => 2,
                a         => 3); # bad
    my %hash = (blah(),
                a         => 2,  # guided by =>
                a         => 3); # bad

A hash substitution is always an even number of arguments,

    my %hash = (a         => 1,
                %blah,           # even number
                a         => 5); # bad, duplicate

"qw()" words are recognised too

    my %hash = (qw(foo value1
                   foo value2));  # bad

Disabling

If you don't care about this you can always disable "ProhibitDuplicateHashKeys" from your .perlcriticrc file in the usual way (see "CONFIGURATION" in Perl::Critic),

    [-ValuesAndExpressions::ProhibitDuplicateHashKeys]

Home page

http://user42.tuxfamily.org/perl-critic-pulp/index.html

Releases

4 releases since Debian 10 (Buster); the text changed 1 time.

10
11–13