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=head1 TITLE
STDIN, STDOUT, STDERR, ARGV, and DATA should become scalars
=head1 VERSION
Maintainer: Nathan Wiger <[EMAIL PROTECTED]>
Date: 04 Aug 2000
Last-Modified: 14 Sep 2000
Mailing List: [EMAIL PROTECTED]
Number: 30
Version: 4
Status: Frozen
=head1 ABSTRACT
Consensus has been reached that filehandles (currently
barewords) will be revamped to become true $scalars, to
make them consistent with other Perl variables.
C<STDIN>, C<STDOUT>, C<STDERR>, and C<DATA> should follow suit and be
renamed C<$STDIN>, C<$STDOUT>, C<$STDERR>, and C<$DATA>, becoming
full-fledged scalar B<fileobjects>. In addition, C<ARGV> should become
C<$ARGV> as well. The old function of C<$ARGV> (the currently open
filename) will be available via polymorphism.
=head1 NOTES ON FREEZE
This was pretty much accepted by everyone, since it follows logically
from filehandles becoming scalars. A few clarifications were added, but
it otherwise remains the same from the previous version.
=head1 DESCRIPTION
=head2 $STDIN, $STDOUT, $STDERR
Currently, filehandles are barewords, such as FILE and
PIPE. However, for Perl 6 these are planned to be renamed
to true "single-whatzitz" types (thanks Tom) and prefixed
with a $. So, the current:
print FILE "$stuff\n";
Will become something like:
print $FILE "$stuff\n";
STDIN, STDOUT, and STDERR need to follow suit. We should
change
print STDERR "$stuff\n";
to:
print $STDERR "$stuff\n";
This makes them consistent with other Perl variables, such
as @ARGV, %ENV, $VERSION, etc, all of which have the correct
distiguishing prefix for their type.
=head2 $DATA
C<DATA> should follow suit, becoming C<$DATA>.
=head2 $ARGV
In addition, C<ARGV> should be renamed to C<$ARGV>. However, this
overlaps with the already-existing C<$ARGV> (currently open filename),
appearing to cause problems. But never fear! Polymorphic objects to the
rescue:
while (<$ARGV>) { # used as fileobject
next if ($ARGV eq $lastfile) # $ARGV->STRING, filename
print "Now reading $ARGV"; # $ARGV->STRING, filename
dostuff($_);
$lastfile = $ARGV; # copies object, but that's ok
# because will have ->STRING too
}
This means that $ARGV will be both the filehandle *and* the name of the
file, but it will automatically morph to suit your needs depending on
context.
Additionally, C<ARGVOUT> should either follow suit, or be wrapped into
C<$ARGV> ($ARGV->OUT?), whichever makes more sense.
=head1 IMPLEMENTATION
All references to these bareword filehandles will have to be changed.
In addition, $STDIN, $STDOUT, and $STDERR should be standard, read-write
variables. If a person wants to do this:
$STDOUT = $myfilehandle;
print "Watch out!";
They should be able to. The same should (probably) go for C<$DATA> and
C<$ARGV>.
=head1 MIGRATION
The p52p6 translator needs to be able to spot instances of barewords and
globs and translate them to scalars:
print STDERR @foo; -> print $STDERR @foo;
dostuff(\*STDIN); -> dostuff($STDIN);
print while(<ARGV>); -> print while(<$ARGV>);
select(STDERR); -> $DEFOUT = $STDERR; # RFC 129
tie *STDOUT, 'Apache'; -> tie Apache $STDOUT; # RFC 200
A similar process will have to be done with all other filehandle
conversions as well, so this may well be handled implicitly by the more
general conversion. We may be able to ignore globs since these should
handle scalars implicitly as aliases.
=head1 REFERENCES
http://www.mail-archive.com/perl6-language@perl.org/msg03279.html
RFC 14: Modify open() to support FileObjects and Extensibility
RFC 159: True Polymorphic Objects
RFC 129: Replace default filehandle/select with $DEFOUT, $DEFERR, $DEFIN
RFC 200: Objects: Revamp tie to support extensibility (Massive tie
changes)
