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 v5.24.1                   Perl::Critic::Policy::ValuesAndExpressions::ProhibitCommaSeparatedStatements(3pm)