Re: PERFORCE change 11142 for review

[p5sagit/p5-mst-13.2.git] / lib / open.pm

diff --git a/lib/open.pm b/lib/open.pm
index da8a044..3a08b79 100644 (file)
--- a/lib/open.pm
+++ b/lib/open.pm
@@ -1,4 +1,45 @@
 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
 
@@ -6,31 +47,52 @@ open - perl pragma to set default disciplines for input and output
 
 =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;