HINT_UTF8 is not propagated to the op tree anymore; add a

perlunicode.pod that reflects changes to unicode support so far

p4raw-id: //depot/perl@4941

1 files changed, 41 insertions, 134 deletions

diff --git a/lib/utf8.pm b/lib/utf8.pm
index 691de0d630..be7cc0bf0c 100644
--- a/lib/utf8.pm
+++ b/lib/utf8.pm
@@ -1,14 +1,15 @@
 package utf8;
 
-$^U = 1;
+$^U = 1 if caller and caller eq 'main';	# they are unicode aware
+					# XXX split this out?
 
 sub import {
-    $^H |= 0x00000008;
+    $^H |= 0x00800000;
     $enc{caller()} = $_[1] if $_[1];
 }
 
 sub unimport {
-    $^H &= ~0x00000008;
+    $^H &= ~0x00800000;
 }
 
 sub AUTOLOAD {
@@ -21,7 +22,7 @@ __END__
 
 =head1 NAME
 
-utf8 - Perl pragma to turn on UTF-8 and Unicode support
+utf8 - Perl pragma to enable/disable UTF-8 in source code
 
 =head1 SYNOPSIS
 
@@ -30,154 +31,60 @@ utf8 - Perl pragma to turn on UTF-8 and Unicode support
 
 =head1 DESCRIPTION
 
-The utf8 pragma tells Perl to use UTF-8 as its internal string
-representation for the rest of the enclosing block.  (The "no utf8"
-pragma tells Perl to switch back to ordinary byte-oriented processing
-for the rest of the enclosing block.)  Under utf8, many operations that
-formerly operated on bytes change to operating on characters.  For
-ASCII data this makes no difference, because UTF-8 stores ASCII in
-single bytes, but for any character greater than C<chr(127)>, the
-character is stored in a sequence of two or more bytes, all of which
-have the high bit set.  But by and large, the user need not worry about
-this, because the utf8 pragma hides it from the user.  A character
-under utf8 is logically just a number ranging from 0 to 2**32 or so.
-Larger characters encode to longer sequences of bytes, but again, this
-is hidden.
+WARNING: The implementation of Unicode support in Perl is incomplete.
+Expect sudden and unannounced changes!
 
-Use of the utf8 pragma has the following effects:
+The C<use utf8> pragma tells the Perl parser to allow UTF-8 in the
+program text in the current lexical scope.  The C<no utf8> pragma
+tells Perl to switch back to treating the source text as literal
+bytes in the current lexical scope.
 
-=over 4
+This pragma is primarily a compatibility device.  Perl versions
+earlier than 5.6 allowed arbitrary bytes in source code, whereas
+in future we would like to standardize on the UTF-8 encoding for
+source text.  Until UTF-8 becomes the default format for source
+text, this pragma should be used to recognize UTF-8 in the source.
+When UTF-8 becomes the standard source format, this pragma will
+effectively become a no-op.
 
-=item *
-
-Strings and patterns may contain characters that have an ordinal value
-larger than 255.  Presuming you use a Unicode editor to edit your
-program, these will typically occur directly within the literal strings
-as UTF-8 characters, but you can also specify a particular character
-with an extension of the C<\x> notation.  UTF-8 characters are
-specified by putting the hexadecimal code within curlies after the
-C<\x>.  For instance, a Unicode smiley face is C<\x{263A}>.  A
-character in the Latin-1 range (128..255) should be written C<\x{ab}>
-rather than C<\xab>, since the former will turn into a two-byte UTF-8
-code, while the latter will continue to be interpreted as generating a
-8-bit byte rather than a character.  In fact, if C<-w> is turned on, it will
-produce a warning that you might be generating invalid UTF-8.
-
-=item *
+Enabling the C<utf8> pragma has the following effects:
 
-Identifiers within the Perl script may contain Unicode alphanumeric
-characters, including ideographs.  (You are currently on your own when
-it comes to using the canonical forms of characters--Perl doesn't (yet)
-attempt to canonicalize variable names for you.)
+=over
 
 =item *
 
-Regular expressions match characters instead of bytes.  For instance,
-"." matches a character instead of a byte.  (However, the C<\C> pattern
-is provided to force a match a single byte ("C<char>" in C, hence
-C<\C>).)
+Bytes in the source text that have their high-bit set will be treated
+as being part of a literal UTF-8 character.  This includes most literals
+such as identifiers, string constants, constant regular expression patterns
+and package names.
 
 =item *
 
-Character classes in regular expressions match characters instead of
-bytes, and match against the character properties specified in the
-Unicode properties database.  So C<\w> can be used to match an ideograph,
-for instance.
+As a side effect, when this pragma is used within the main package,
+it also enables Unicode character semantics for the entire program.
+See L<perlunicode> for more on that.
 
-=item *
-
-Named Unicode properties and block ranges make be used as character
-classes via the new C<\p{}> (matches property) and C<\P{}> (doesn't
-match property) constructs.  For instance, C<\p{Lu}> matches any
-character with the Unicode uppercase property, while C<\p{M}> matches
-any mark character.  Single letter properties may omit the brackets, so
-that can be written C<\pM> also.  Many predefined character classes are
-available, such as C<\p{IsMirrored}> and  C<\p{InTibetan}>.
+[XXX: split this out into separate "pragma" and/or -C command-line
+switch?]
 
 =item *
 
-The special pattern C<\X> match matches any extended Unicode sequence
-(a "combining character sequence" in Standardese), where the first
-character is a base character and subsequent characters are mark
-characters that apply to the base character.  It is equivalent to
-C<(?:\PM\pM*)>.
-
-=item *
+In the absence of inputs marked as UTF-8, regular expressions within the
+scope of this pragma will default to using character semantics instead
+of byte semantics.
 
-The C<tr///> operator translates characters instead of bytes.  It can also
-be forced to translate between 8-bit codes and UTF-8 regardless of the
-surrounding utf8 state.  For instance, if you know your input in Latin-1,
-you can say:
-
-    use utf8;
-    while (<>) {
-	tr/\0-\xff//CU;		# latin1 char to utf8
-	...
+    @bytes_or_chars = split //, $data;	# may split to bytes if data
+					# $data isn't UTF-8
+    {
+	use utf8;			# force char semantics
+	@chars = split //, $data;	# splits characters
     }
 
-Similarly you could translate your output with
-
-    tr/\0-\x{ff}//UC;		# utf8 to latin1 char
-
-No, C<s///> doesn't take /U or /C (yet?).
-
-=item *
-
-Case translation operators use the Unicode case translation tables.
-Note that C<uc()> translates to uppercase, while C<ucfirst> translates
-to titlecase (for languages that make the distinction).  Naturally
-the corresponding backslash sequences have the same semantics.
-
-=item *
-
-Most operators that deal with positions or lengths in the string will
-automatically switch to using character positions, including C<chop()>,
-C<substr()>, C<pos()>, C<index()>, C<rindex()>, C<sprintf()>,
-C<write()>, and C<length()>.  Operators that specifically don't switch
-include C<vec()>, C<pack()>, and C<unpack()>.  Operators that really
-don't care include C<chomp()>, as well as any other operator that
-treats a string as a bucket of bits, such as C<sort()>, and the
-operators dealing with filenames.
-
-=item *
-
-The C<pack()>/C<unpack()> letters "C<c>" and "C<C>" do I<not> change,
-since they're often used for byte-oriented formats.  (Again, think
-"C<char>" in the C language.)  However, there is a new "C<U>" specifier
-that will convert between UTF-8 characters and integers.  (It works
-outside of the utf8 pragma too.)
-
-=item *
-
-The C<chr()> and C<ord()> functions work on characters.  This is like
-C<pack("U")> and C<unpack("U")>, not like C<pack("C")> and
-C<unpack("C")>.  In fact, the latter are how you now emulate
-byte-oriented C<chr()> and C<ord()> under utf8.
-
-=item *
-
-And finally, C<scalar reverse()> reverses by character rather than by byte.
-
-=back
-
-=head1 CAVEATS
-
-As of yet, there is no method for automatically coercing input and
-output to some encoding other than UTF-8.  This is planned in the near
-future, however.
+[XXX: Should this should be enabled like chr()/sprintf("%c") by looking
+at $^U instead?]
 
-In any event, you'll need to keep track of whether interfaces to other
-modules expect UTF-8 data or something else.  The utf8 pragma does not
-magically mark strings for you in order to remember their encoding, nor
-will any automatic coercion happen (other than that eventually planned
-for I/O).  If you want such automatic coercion, you can build yourself
-a set of pretty object-oriented modules.  Expect it to run considerably
-slower than than this low-level support.
+=head1 SEE ALSO
 
-Use of locales with utf8 may lead to odd results.  Currently there is
-some attempt to apply 8-bit locale info to characters in the range
-0..255, but this is demonstrably incorrect for locales that use
-characters above that range (when mapped into Unicode).  It will also
-tend to run slower.  Avoidance of locales is strongly encouraged.
+L<perlunicode>, L<byte>
 
 =cut