NAME

       Perl::Critic::Policy::ValuesAndExpressions::UnexpandedSpecialLiteral - specials like
       __PACKAGE__ used literally

DESCRIPTION

       This policy is part of the "Perl::Critic::Pulp" add-on.  It picks up some cases where the
       special literals "__FILE__", "__LINE__" and "__PACKAGE__" (see "Special Literals" in
       perldata) are used with "=>" or as a hash subscript and so don't expand to the respective
       filename, line number or package name.

           my $seen = { __FILE__ => 1 };          # bad
           return ('At:'.__LINE__ => 123);        # bad
           $obj->{__PACKAGE__}->{myextra} = 123;  # bad

       In each case you get a string "__FILE__", "__LINE__" or "__PACKAGE__", as if

           my $seen = { '__FILE__' => 1 };
           return ('At:__LINE__' => 123);
           $obj->{'__PACKAGE__'}->{'myextra'} = 123;

       where almost certainly it was meant to expand to the filename etc.  On that basis this
       policy is under the "bugs" theme (see "POLICY THEMES" in Perl::Critic).

       Expression forms like

           'MyExtra::'.__PACKAGE__ => 123    # bad

       are still bad because the word immediately to the left of a "=>" is quoted even when that
       word is part of an expression.

       If you really do want a string "__FILE__" etc then the suggestion is to write the quotes,
       even if you're not in the habit of using quotes in hash constructors etc.  It'll pass this
       policy and make it clear to everyone that you really did want the literal string.

       The "__PACKAGE__" literal is new in Perl 5.004 but this policy is applied to all code.
       Even if you're targeting an earlier Perl extra quotes will make it clear to users of later
       Perl that a literal string "__PACKAGE__" is indeed intended.

   Fat Comma After Newline
       A "=>" fat comma only quotes when it's on the same line as the preceding bareword, so in
       the following "__PACKAGE__" is not quoted and is therefore not reported by this policy,

           my %hash = (__PACKAGE__   # ok, expands
                       =>
                       'blah');

       Of course whether or not writing this is a good idea is another matter.  It might be a bit
       subtle to depend on the newline.  Probably a plain "," comma would make the intention
       clearer than "=>".

   Class Data
       A bad "$obj->{__PACKAGE__}" can arise when you're trying to hang extra data on an object
       using your package name to hopefully not clash with the object's native fields.
       Unexpanded "__PACKAGE__" like that is a mistake you'll probably only make once; after that
       the irritation of writing extra parens or similar will keep it fresh in your mind!

       As usual there's more than one way to do it when associating extra data to an object.  As
       a crib here are some ways,

       Subhash "$obj->{(__PACKAGE__)}->{myfield}"
           The extra parens ensure expansion, and you get a sub-hash (or sub-array or whatever)
           to yourself.  It's easy to delete the single entry from $obj if/when you later want to
           cleanup.

       Subscript "$obj->{__PACKAGE__,'myfield'}"
           This makes entries in $obj, with the $; separator emulating multidimensional
           arrays/hashes (see "$;" in perlvar).

       Concated key "$obj->{__PACKAGE__.'--myfield'}"
           Again entries in $obj, but key formed by concatenation and an explicit unlikely
           separator.  The advantage over "," is that the key is a constant (after constant
           folding), instead of a "join" on every access because $; could change.

       Separate "Tie::HashRef::Weak"
           Use the object as a hash key and the value whatever data you want to associate.  Keeps
           completely out of the object's hair and also works with objects which use a
           "restricted hash" (see Hash::Util) to prevent extra keys.

       Inside-Out "Hash::Util::FieldHash"
           Similar to HashRef with object as key and any value you want as the data outside the
           object, hence the jargon "inside out".  The docs are very hard to follow (as of its
           version 1.04), especially if you're not into OOP, but it's actually fairly simple.

       "Scalar::Footnote"
           Key/value pairs attached to an object using its "magic" list.  Doesn't touch the
           object's contents but separate footnote users must be careful not to let their keys
           clash.

SEE ALSO

       Perl::Critic::Pulp, Perl::Critic, "Special Literals" in perldata

HOME PAGE

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

COPYRIGHT

       Copyright 2008, 2009, 2010, 2011, 2012, 2013, 2014, 2015, 2016, 2017, 2019, 2021 Kevin
       Ryde

       Perl-Critic-Pulp is free software; you can redistribute it and/or modify it under the
       terms of the GNU General Public License as published by the Free Software Foundation;
       either version 3, or (at your option) any later version.

       Perl-Critic-Pulp is distributed in the hope that it will be useful, but WITHOUT ANY
       WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR
       PURPOSE.  See the GNU General Public License for more details.

       You should have received a copy of the GNU General Public License along with Perl-Critic-
       Pulp.  If not, see <http://www.gnu.org/licenses/>.

perl v5.32.1            Perl::Critic::Policy::ValuesAndExpressions::UnexpandedSpecialLiteral(3pm)