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
=head1 SYNOPSIS
- use open IN => ":any", OUT => ":utf8"; # unimplemented
+ use open IN => ":crlf", OUT => ":raw";
=head1 DESCRIPTION
-NOTE: This pragma is not yet implemented.
+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.
-The open pragma is used to declare one or more default disciplines for
-I/O operations. Any constructors for file, socket, pipe, or directory
-handles found within the lexical scope of this pragma will use the
-declared default.
+Directory handles may also support disciplines in future.
-Handle constructors that are called with an explicit set of disciplines
-are not influenced by the declared defaults.
+=head1 NONPERLIO FUNCTIONALITY
-The default disciplines so declared are available by the special
-discipline name ":def", and can be used within handle constructors
-that allow disciplines to be specified. This makes it possible to
-stack new disciplines over the default ones.
+If Perl is not built to use PerlIO as its IO system then only the two
+pseudo-disciplines ":raw" and ":crlf" are available.
- open FH, "<:para :def", $file or die "can't open $file: $!";
+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<perlunicode>, L<perlfunc/"open">
+L<perlfunc/"binmode">, L<perlfunc/"open">, L<perlunicode>, L<PerlIO>
=cut
-
-1;