Kevin Ryde > Perl-Critic-Pulp > Perl::Critic::Policy::ValuesAndExpressions::ProhibitNullStatements

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NAME ^

Perl::Critic::Policy::ValuesAndExpressions::ProhibitNullStatements - disallow empty statements (stray semicolons)

DESCRIPTION ^

This policy is part of the Perl::Critic::Pulp add-on. It prohibits empty statements, ie. bare ; semicolons. This can be a typo doubling up a semi like

    use Foo;;    # bad

Or a stray left at the end of a control structure like

    if ($foo) {
      print "foo\n";
      return;
    };           # bad

An empty statement is completely harmless, so this policy is only under the "cosmetic" theme (see "POLICY THEMES" in Perl::Critic). It's surprisingly easy to leave a semi behind when chopping code around, especially when changing a statement to a loop or conditional.

Allowed forms

A C style for (;;) { ...} loop is ok. Those semicolons are expression separators and empties are quite usual.

    for (;;) {   # ok
      print "infinite loop\n";
    }

A semicolon at the start of a map or grep block is allowed. It's commonly used to ensure Perl parses it as a block, not an anonymous hash. (Perl decides at the point it parses the {. A ; there forces a block when it might otherwise guess wrongly. See "map" in perlfunc for more on this.)

    map {; $_, 123} @some_list;      # ok

    grep {# this is a block
          ;                          # ok
          length $_ and $something } @some_list;

The map form is much more common than the grep, but both suffer the same ambiguity. grep doesn't normally inspire people to quite such wildly convoluted forms as map does.

CONFIGURATION ^

allow_perl4_semihash (boolean, default false)

If true then Perl 4 style documentation comments like the following are allowed.

    ;# Usage: 
    ;#      require 'mypkg.pl';
    ;#      ...

The ; must be at the start of the line. This is fairly outdated, so it's disabled by default. If you're crunching through some old code you can enable it by adding to your .perlcriticrc file

    [ValuesAndExpressions::ProhibitNullStatements]
    allow_perl4_semihash=1

SEE ALSO ^

Perl::Critic::Pulp, Perl::Critic

HOME PAGE ^

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

COPYRIGHT ^

Copyright 2008, 2009, 2010, 2011, 2012, 2013, 2014 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/>.

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