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Perl-Critic-Pulp-99
River stage two • 5 direct dependents • 18 total dependents
4 ++
/ Perl::Critic::Policy::ValuesAndExpressions::ProhibitNullStatements

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 harmless, so this policy is under the "cosmetic" theme (see "POLICY THEMES" in Perl::Critic) and medium severity. 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 there 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 convoluted forms as map does.

Try/Catch Blocks

The Try, TryCatch and Syntax::Feature::Try modules all add new try block statement forms. These statements don't require a terminating semicolon (the same as an if doesn't require one). Any semicolon there is reckoned as a null statement.

    use TryCatch;
    sub foo {
      try { attempt_something() }
      catch { error_recovery()  };   # bad
    }

This doesn't apply to other try modules such as Try::Tiny and friends. They're implemented as ordinary function calls (with prototypes), so a terminating semicolon is normal for them.

    use Try::Tiny;
    sub foo {
      try { attempt_something() }
      catch { error_recovery()  };   # ok
    }

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, Perl::Critic::Policy::CodeLayout::RequireFinalSemicolon

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/>.