Perl::Critic::Policy::ValuesAndExpressions::ProhibitCommaSeparatedStatements(3))
NAMEPerl::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::Critic::Policy::ValuesAndExpressions::ProhibitCommaSeparatedStatements(3)
