NAME

       Perl::Critic::Policy::ValuesAndExpressions::ProhibitCommaSeparatedStatements - Don't use
       the comma operator as a statement separator.

AFFILIATION

       This Policy is part of the core Perl::Critic distribution.

DESCRIPTION

       Perl's comma statement separator has really low precedence, which leads to code that looks
       like it's using the comma list element separator not actually doing so.  Conway suggests
       that the statement separator not be used in order to prevent this situation.

       The confusion that the statement separator causes is primarily due to the assignment
       operators having higher precedence.

       For example, trying to combine two arrays into another like this won't work:

           @x = @y, @z;

       because it is equivalent to

           @x = @y;
           @z;

       Conversely, there are the built-in functions, like "print", that normally force the rest
       of the statement into list context, but don't when called like a subroutine.

       This is not likely to produce what is intended:

           print join q{, }, 2, 3, 5, 7, ": the single-digit primes.\n";

       The obvious fix is to add parentheses.  Placing them like

           print join( q{, }, 2, 3, 5, 7 ), ": the single-digit primes.\n";

       will work, but

           print ( join q{, }, 2, 3, 5, 7 ), ": the single-digit primes.\n";

       will not, because it is equivalent to

           print( join q{, }, 2, 3, 5, 7 );
           ": the single-digit primes.\n";

CONFIGURATION

       This policy can be configured to allow the last statement in a "map" or "grep" block to be
       comma separated.  This is done via the
       "allow_last_statement_to_be_comma_separated_in_map_and_grep" option like so:

           [ValuesAndExpressions::ProhibitCommaSeparatedStatements]
           allow_last_statement_to_be_comma_separated_in_map_and_grep = 1

       With this option off (the default), the following code violates this policy.

           %hash = map {$_, 1} @list;

       With this option on, this statement is allowed.  Even if this option is off, using a fat
       comma "=>" works, but that forces stringification on the first value, which may not be
       what you want.

BUGS

       Needs to check for "scalar( something, something )".

AUTHOR

       Elliot Shank "<perl@galumph.com>"

COPYRIGHT

       Copyright (c) 2007-2011 Elliot Shank.

       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.

perl v5.20.2    Perl::Critic::Policy::ValuesAndExpressions::ProhibitCommaSeparatedStatements(3pm)