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package open;
use Carp;
$open::hint_bits = 0x20000;
our $VERSION = '1.01';
sub import {
my ($class,@args) = @_;
croak("`use open' needs explicit list of disciplines") unless @args;
$^H |= $open::hint_bits;
my ($in,$out) = split(/\0/,(${^OPEN} || '\0'));
my @in = split(/\s+/,$in);
my @out = split(/\s+/,$out);
while (@args) {
my $type = shift(@args);
my $discp = shift(@args);
my @val;
foreach my $layer (split(/\s+/,$discp)) {
$layer =~ s/^://;
unless(PerlIO::Layer::->find($layer)) {
carp("Unknown discipline layer '$layer'");
}
push(@val,":$layer");
if ($layer =~ /^(crlf|raw)$/) {
$^H{"open_$type"} = $layer;
}
}
if ($type eq 'IN') {
$in = join(' ',@val);
}
elsif ($type eq 'OUT') {
$out = join(' ',@val);
}
else {
croak "Unknown discipline class '$type'";
}
}
${^OPEN} = join('\0',$in,$out);
}
1;
__END__
=head1 NAME
open - perl pragma to set default disciplines for input and output
=head1 SYNOPSIS
use open IN => ":crlf", OUT => ":raw";
=head1 DESCRIPTION
Full-fledged support for I/O disciplines is now implemented provided
Perl is configured to use PerlIO as its IO system (which is now the
default).
The C<open> pragma serves as one of the interfaces to declare default
"layers" (aka disciplines) for all I/O.
The C<open> pragma is used to declare one or more default layers for
I/O operations. Any open(), readpipe() (aka qx//) and similar
operators found within the lexical scope of this pragma will use the
declared defaults.
When open() is given an explicit list of layers they are appended to
the list declared using this pragma.
Directory handles may also support disciplines in future.
=head1 NONPERLIO FUNCTIONALITY
If Perl is not built to use PerlIO as its IO system then only the two
pseudo-disciplines ":raw" and ":crlf" are available.
The ":raw" discipline corresponds to "binary mode" and the ":crlf"
discipline corresponds to "text mode" on platforms that distinguish
between the two modes when opening files (which is many DOS-like
platforms, including Windows). These two disciplines are no-ops on
platforms where binmode() is a no-op, but perform their functions
everywhere if PerlIO is enabled.
=head1 IMPLEMENTATION DETAILS
There is a class method in C<PerlIO::Layer> C<find> which is implemented as XS code.
It is called by C<import> to validate the layers:
PerlIO::Layer::->find("perlio")
The return value (if defined) is a Perl object, of class C<PerlIO::Layer> which is
created by the C code in F<perlio.c>. As yet there is nothing useful you can do with the
object at the perl level.
=head1 SEE ALSO
L<perlfunc/"binmode">, L<perlfunc/"open">, L<perlunicode>, L<PerlIO>
=cut
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