package open;
+use Carp;
+$open::hint_bits = 0x20000;
+
+# layers array and hash mainly manipulated by C code in perlio.c
+use vars qw(%layers @layers);
+
+# Populate hash in non-PerlIO case
+%layers = (crlf => 1, raw => 0) unless (@layers);
+
+# warn join(',',keys %layers);
+
+our $VERSION = '1.00';
+
+sub import {
+ my ($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(exists $layers{$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: $!";
+The ":raw" discipline corresponds to "binary mode" and the ":crlf"
+discipline corresponds to "text mode" on platforms that distinguish
+between the two modes when opening files (which is many DOS-like
+platforms, including Windows). These two disciplines are
+no-ops on platforms where binmode() is a no-op, but perform their
+functions everywhere if PerlIO is enabled.
+
+=head1 IMPLEMENTATION DETAILS
+
+There are two package variables C<%layers> and C<@layers> which
+are mainly manipulated by C code in F<perlio.c>, but are visible
+to the nosy:
+
+ print "Have ",join(',',keys %open::layers),"\n";
+ print "Using ",join(',',@open::layers),"\n";
+
+The C<%open::layers> hash is a record of the available "layers" that may be pushed
+onto a C<PerlIO> stream. The values of the hash are perl objects, of class C<PerlIO::Layer>
+which are created by the C code in F<perlio.c>. As yet there is nothing useful you
+can do with the objects at the perl level.
+
+The C<@open::layers> array is the current set of layers and their arguments.
+The array consists of layer => argument pairs and I<must> always have even number of
+entries and the even entries I<must> be C<PerlIO::Layer> objects or perl will "die"
+when it attempts to open a filehandle. In most cases the odd entry will be C<undef>,
+but in the case of (say) ":encoding(iso-8859-1)" it will be 'iso-8859-1'. These
+argument entries are currently restricted to being strings.
+
+When a new C<PerlIO> stream is opened, the C code looks at the
+array to determine the default layers to be pushed. So with care it is possible
+to manipulate the default layer "stack":
+
+ splice(@PerlIO::layers,-2,2);
+ push(@PerlIO::layers,$PerlIO::layers{'stdio'} => undef);
=head1 SEE ALSO
-L<perlunicode>, L<perlfunc/"open">
+L<perlfunc/"binmode">, L<perlfunc/"open">, L<perlunicode>, L<PerlIO>
=cut
-
-1;
projects / p5sagit/p5-mst-13.2.git / blobdiff