[perl #96592] 4 pod casemapping errors: s/(\w+)/\u\L$1/g is ALWAYS WRONG

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These are all in error:

    perldata.pod:        s/(\w+)/\u\L$1/g;   # "titlecase" words
    perlfaq4.pod:	$string =~ s/([\w']+)/\u\L$1/g;
    perlop.pod:    substr($str, -30) =~ s/\b(\p{Alpha}+)\b/\u\L$1/g;
    perlretut.pod:string. The regexps C<\L\u$word> or C<\u\L$word> convert the first

They don't work because you cannot guarantee a correct titlecase
mapping if you first send it through lowercase.  There are no 
roundtrip guarantees with Unicode casemapping.

Here are two places where you get an error doing it the way
the pods erroneously suggest, but there are others:

    orig  => İ is 0130
       lc => i̇ is 0069.0307
    tc    => İ is 0130
    tc lc => İ is 0049.0307     (wrong answer)

    orig  => ẞ is 1E9E
       lc => ß is 00DF
    tc    => ẞ is 1E9E
    tc lc => Ss is 0053.0073    (wrong answer)

The correct approach requires something more like

    s/\b(\w)(\w*)\b/\u$1\L$2/g;  # "titlecase" "words"

Because casemapA(string) is never guaranteed to be the
same as casemapA(casemapB(string)).  

--tom

#!/usr/bin/env perl

use utf8;

use v5.14;
use strict;
use warnings;
use open qw(:std :encoding(UTF-8));
use charnames qw(:full);

my @chars = (
    "\N{LATIN CAPITAL LETTER I WITH DOT ABOVE}",
    "\N{GREEK CAPITAL THETA SYMBOL}",
    "\N{LATIN CAPITAL LETTER SHARP S}",
    "\N{OHM SIGN}",
    "\N{KELVIN SIGN}",
    "\N{ANGSTROM SIGN}",

    "\N{LATIN SMALL LETTER SHARP S}",
    "\N{GREEK SMALL LETTER ALPHA WITH PSILI AND YPOGEGRAMMENI}",
    "\N{LATIN SMALL LIGATURE FF}",
    "\N{LATIN SMALL LIGATURE FFI}",
    "\N{LATIN SMALL LIGATURE LONG S T}",
    "\N{LATIN SMALL LIGATURE ST}",
);

sub report($$;$) { 
    my ($what, $str, $ok) = @_;
    my $mask = "%-5s => %-3s is %v04X\n";
    if (@_ == 3) {
        $mask =~ s/\n/\t%s\n/;
    } 
    printf $mask, $what, ($str) x 2, $ok;
}

for my $char (@chars) {
    my $lc         =         lc $char;
    my $tc_good    = ucfirst    $char;
    my $tc_bad_lc  = ucfirst lc $char;
    my $tc_bad_uc  = ucfirst uc $char;

    report "orig " => $char;
    report "   lc" => $lc;
    report "tc   " => $tc_good,   "real";
    report "tc lc" => $tc_bad_lc, ($tc_good eq $tc_bad_lc) ? "RIGHT" : "WRONG";
    report "tc uc" => $tc_bad_uc, ($tc_good eq $tc_bad_uc) ? "RIGHT" : "WRONG";
    print "\n";
}

__END__

Summary of my perl5 (revision 5 version 14 subversion 0) configuration:
   
  Platform:
    osname=openbsd, osvers=4.4, archname=OpenBSD.i386-openbsd
    uname='openbsd chthon 4.4 generic#0 i386 '
    config_args='-des'
    hint=recommended, useposix=true, d_sigaction=define
    useithreads=undef, usemultiplicity=undef
    useperlio=define, d_sfio=undef, uselargefiles=define, usesocks=undef
    use64bitint=undef, use64bitall=undef, uselongdouble=undef
    usemymalloc=y, bincompat5005=undef
  Compiler:
    cc='cc', ccflags ='-fno-strict-aliasing -pipe -fstack-protector -I/usr/local/include',
    optimize='-O2',
    cppflags='-fno-strict-aliasing -pipe -fstack-protector -I/usr/local/include'
    ccversion='', gccversion='3.3.5 (propolice)', gccosandvers='openbsd4.4'
    intsize=4, longsize=4, ptrsize=4, doublesize=8, byteorder=1234
    d_longlong=define, longlongsize=8, d_longdbl=define, longdblsize=12
    ivtype='long', ivsize=4, nvtype='double', nvsize=8, Off_t='off_t', lseeksize=8
    alignbytes=4, prototype=define
  Linker and Libraries:
    ld='cc', ldflags ='-Wl,-E  -fstack-protector -L/usr/local/lib'
    libpth=/usr/local/lib /usr/lib
    libs=-lgdbm -lm -lutil -lc
    perllibs=-lm -lutil -lc
    libc=/usr/lib/libc.so.48.0, so=so, useshrplib=false, libperl=libperl.a
    gnulibc_version=''
  Dynamic Linking:
    dlsrc=dl_dlopen.xs, dlext=so, d_dlsymun=undef, ccdlflags=' '
    cccdlflags='-DPIC -fPIC ', lddlflags='-shared -fPIC  -L/usr/local/lib -fstack-protector'


Characteristics of this binary (from libperl): 
  Compile-time options: MYMALLOC PERL_DONT_CREATE_GVSV PERL_MALLOC_WRAP
                        PERL_PRESERVE_IVUV USE_LARGE_FILES USE_PERLIO
                        USE_PERL_ATOF
  Built under openbsd
  Compiled at Jun 11 2011 11:48:28
  %ENV:
    PERL_UNICODE="SA"
  @INC:
    /usr/local/lib/perl5/site_perl/5.14.0/OpenBSD.i386-openbsd
    /usr/local/lib/perl5/site_perl/5.14.0
    /usr/local/lib/perl5/5.14.0/OpenBSD.i386-openbsd
    /usr/local/lib/perl5/5.14.0
    /usr/local/lib/perl5/site_perl/5.12.3
    /usr/local/lib/perl5/site_perl/5.11.3
    /usr/local/lib/perl5/site_perl/5.10.1
    /usr/local/lib/perl5/site_perl/5.10.0
    /usr/local/lib/perl5/site_perl/5.8.7
    /usr/local/lib/perl5/site_perl/5.8.0
    /usr/local/lib/perl5/site_perl/5.6.0
    /usr/local/lib/perl5/site_perl/5.005
    /usr/local/lib/perl5/site_perl
    .

• [perl #96592] 4 pod casemapping errors: s/(\w+)/\u\L$1/g is ALWAYS WRONG by tchrist1