Front page | perl.perl6.language.flow |
Postings from August 2000
This and other RFCs are available on the web at
http://dev.perl.org/rfc/
=head1 TITLE
Implicit counter in C<for> statements, possibly C<$#>.
=head1 VERSION
Maintainer: John McNamara <jmcnamara@cpan.org>
Date: 16 Aug 2000
Version: 1
Mailing List: perl6-language-flow@perl.org
Number: 120
=head1 ABSTRACT
The syntax of Perl style C<for> statements could be simplified by the introduction of an implicit counter variable. The deprecated variable C<$#> could be used for this purpose due to its mnemonic association with C<$#array>.
=head1 DESCRIPTION
The following discussion make no differentiation between the C<for> and C<foreach> statements.
The use of the C<foreach> statement or the C<for> statement in conjunction with the range operator, C<..>, are generally seen as good idiomatic Perl:
@array = qw(sun moon stars rain);
foreach $item (@array) {
print $item, "\n";
}
as opposed to the "endearing attachment to C" style:
for ($i = 0; $i <= $#array; $i++) {
print $array[$i], "\n";
}
However, the latter format is often more convenient if you need to keep track of the array index as well as iterating over the array:
for ($i = 0; $i <= $#array; $i++) {
print $array[$i], " is at index ", $i, "\n";
}
is more succinct than:
$i = 0;
foreach $item (@array) {
print $item, " is at index ", $i, "\n";
$i++;
}
The addition of an implicit counter variable in C<for> statements would lead to a more elegant syntax. It is proposed that the deprecated variable C<$#> should be used for this purpose due to its mnemonic association with C<$#array>. For example:
foreach $item (@array) {
print $item, " is at index ", $#, "\n";
}
The variable C<$#> currently holds the output format for printed numbers.
=head1 IMPLEMENTATION
Not sure. However, consideration would have to be given to nested C<for> statements and how the variable would be affected by C<local>.
=head1 REFERENCES
perldoc perlvar
Alex Rhomberg proposed an implicit counter variable on clpm:
http://x53.deja.com/getdoc.xp?AN=557218804&fmt=text and
http://x52.deja.com/threadmsg_ct.xp?AN=580369190.1&fmt=text
Craig Berry suggested C<$#>:
http://x52.deja.com/threadmsg_ct.xp?AN=580403316.1&fmt=text
Thread Next