Would Perl use fc over uc?

Question

When will you ever need to use fc(), when uc()will it ever fail?

Perl fc documentation

Answer 1

fc used for case insensitivity.

uc($a) cmp uc($b)    # XXX
lc($a) cmp lc($b)    # XXX
fc($a) cmp fc($b)    # ok

An example where it matters:

   lc uc fc
-- -- -- --
ss ss SS ss
SS ss SS ss
ß  ß  SS ss
ẞ  ß  ẞ  ss

Note that fc ("ß") eq fc ("ẞ"), but uc ("ß") ne uc ("ẞ").

Note that fc ("ß") eq fc ("ss"), but lc ("ß") ne lc ("ss").

---

The table was generated using

use strict;
use warnings;
use feature qw( fc );

use open ':std', ':encoding(UTF-8)';

my $ss = "\N{LATIN SMALL LETTER SHARP S}";
my $SS = "\N{LATIN CAPITAL LETTER SHARP S}";

printf("   lc uc fc\n");
printf("-- -- -- --\n");
printf("%-2s %-2s %-2s %-2s\n", $_, lc($_), uc($_), fc($_))
   for 'ss', 'SS', $ss, $SS;