This and other RFCs are available on the web at http://dev.perl.org/rfc/ =head1 TITLE Allow multiple loop variables in foreach statements =head1 VERSION Maintainer: Peter Scott <[EMAIL PROTECTED]> Date: 29 Aug 2000 Last Modified: 6 Sep 2000 Mailing List: [EMAIL PROTECTED] Version: 2 Number: 173 Status: Frozen =head1 ABSTRACT Allow for a list of loop variables in for(each) statements, i.e. & e.g., foreach my ($x, $y, $z) (@list) { ... } =head1 DESCRIPTION This has been raised by several people in the past, most recently on the perl6-* lists by Graham Barr, who does not have time to RFC it currently. The semantics are (hopefully) obvious: where foreach $var (@list) iterates through C<@list>, assigning C<$var> to each element in turn, foreach ($var_1, ... $var_n) (@list) iterates through C<@list> n elements at a time, assigning C<$var_1> through C<$var_n> to them respectively. If the number of elements in C<@list> is not evenly divisible by n, the remaining loop variables on the last iteration become C<undef>. The most obvious usefulness is traversing a hash which has been passed in an argument list: sub foo { foreach my($key, $value) (@_) { ... } } foo(%hash); instead of having to make a temporary copy: sub foo { my %h = @_; while (my ($key, $value) = each %h) { ... } } This extension does not apply to the C<foreach> statement I<modifier>, since that doesn't accept a loop variable anyway. =head2 Alternatives While C<splice> is frequently adduced as an alternative, this requires an array instead of just a list, and is destructive to boot. =head1 IMPLEMENTATION The potential parsing difficulty I came up with was how to tell that foreach ($a,$b,$c) (@list) ... was not foreach $_ ($a, $b, $c) (@list) ... Graham tells me that the required parentheses and block braces make it possible for the parser to be able to tell the difference. John Porter suggests an alternative syntax foreach [$a, $b, $c] (@list) which could be employed instead if there is a parsing problem. =head1 REFERENCES L<perlsyn/"Foreach Loops">
