#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

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.