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 $VERSION = '1.00';
+
sub import {
- shift;
- die "`use open' needs explicit list of disciplines" unless @_;
+ my ($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 (@_) {
- my $type = shift;
- my $discp = shift;
+ while (@args) {
+ my $type = shift(@args);
+ my $discp = shift(@args);
my @val;
- foreach my $layer (split(/\s+:?/,$discp)) {
+ foreach my $layer (split(/\s+/,$discp)) {
+ $layer =~ s/^://;
unless(exists $layers{$layer}) {
- croak "Unknown discipline layer '$layer'";
+ carp("Unknown discipline layer '$layer'");
}
push(@val,":$layer");
if ($layer =~ /^(crlf|raw)$/) {
=head1 DESCRIPTION
-The open pragma is used to declare one or more default disciplines for
-I/O operations. Any open() and readpipe() (aka qx//) operators found
-within the lexical scope of this pragma will use the declared defaults.
-Neither open() with an explicit set of disciplines, nor sysopen() are
-influenced by this pragma.
+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.
-Only the two pseudo-disciplines ":raw" and ":crlf" are currently
-available.
+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 currently
-no-ops on platforms where binmode() is a no-op, but will be
-supported everywhere in future.
+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
-=head1 UNIMPLEMENTED FUNCTIONALITY
+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:
-Full-fledged support for I/O disciplines is currently unimplemented.
-When they are eventually supported, this pragma will serve as one of
-the interfaces to declare default disciplines for all I/O.
+ print "Have ",join(',',keys %open::layers),"\n";
+ print "Using ",join(',',@open::layers),"\n";
-In future, any default disciplines declared by this pragma will be
-available by the special discipline name ":DEFAULT", and could be used
-within handle constructors that allow disciplines to be specified.
-This would make it possible to stack new disciplines over the default
-ones.
+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.
- open FH, "<:para :DEFAULT", $file or die "can't open $file: $!";
+The C<@open::layers> array is the current set of layers and their arguments.
+The array consists of layer => argument pairs and I<must> always have even number of
+entries and the even entries I<must> be C<PerlIO::Layer> objects or perl will "die"
+when it attempts to open a filehandle. In most cases the odd entry will be C<undef>,
+but in the case of (say) ":encoding(iso-8859-1)" it will be 'iso-8859-1'. These
+argument entries are currently restricted to being strings.
-Socket and directory handles will also support disciplines in
-future.
+When a new C<PerlIO> stream is opened, the C code looks at the
+array to determine the default layers to be pushed. So with care it is possible
+to manipulate the default layer "stack":
-Full support for I/O disciplines will enable all of the supported
-disciplines to work on all platforms.
+ splice(@PerlIO::layers,-2,2);
+ push(@PerlIO::layers,$PerlIO::layers{'stdio'} => undef);
=head1 SEE ALSO
-L<perlfunc/"binmode">, L<perlfunc/"open">, L<perlunicode>
+L<perlfunc/"binmode">, L<perlfunc/"open">, L<perlunicode>, L<PerlIO>
=cut
projects / p5sagit/p5-mst-13.2.git / blobdiff