NAME

       Unicode::CaseFold - Unicode case-folding for case-insensitive lookups.

VERSION

       version 1.01

SYNOPSIS

           use Unicode::CaseFold;

           my $folded = fc $string;

   What is Case-Folding?
       In non-Unicode contexts, a common idiom to compare two strings case-insensitively is
       "lc($this) eq lc($that)". Before comparing two strings we normalize them to an all-
       lowercase version. "Hello", "HELLO", and "HeLlO" all have the same lowercase form
       ("hello"), so it doesn't matter which one we start with; they are all equal to one another
       after "lc".

       In Unicode, things aren't so simple. A Unicode character might have mappings for
       uppercase, lowercase, and titlecase, and the lowercase mapping of the uppercase mapping of
       a given character might not be the character that you started with! For example
       "lc(uc("\N{LATIN SMALL LETTER SHARP S"))" is "ss", not the eszett we started off with!
       Case-folding is a part of the Unicode standard that allows any two strings that differ
       from one another only by case to map to the same "case-folded" form, even when those
       strings include characters with complex case-mappings.

   Use for Case-insensitive Comparison
       Simply write "fc($this) eq fc($that)" instead of "lc($this) eq lc($that)".  You can also
       use "index" on case-folded strings for substring search.

   Use for String Lookups
       Frequently we want to store data in a hash, or a database, or an external file for later
       retrieval. Sometimes we want to be able to match the keys in this data case-insensitively
       -- that is, we should be able to store some data under the key "hello" and later retrieve
       it with the key "HELLO". Some databases have complete support for collation, but in other
       databases the support is missing or broken, and Perl hashes don't support it at all. By
       making case-folding part of the process you use to normalize your keys before using them
       to access a database or data structure, you get case-insensitive lookup.

           $roles{fc "Samuel L. Jackson"} = ["Gin Rummy", "Nick Fury", "Mace Windu"];

           $roles = $roles{fc "Samuel l. JACKSON"}; # Gets the data.

DESCRIPTION

       This module provides Unicode case-folding for Perl. Case-folding is a tool that allows a
       program to make case-insensitive string comparisons or do case-insensitive lookups.

EXPORTS

   fc($str)
       Exported by default when you use the module. "use Unicode::CaseFold ()" or "use
       Unicode::CaseFold qw(case_fold !fc)" if you don't want it to be exported.

       Returns the case-folded version of $str. This function is prototyped to act as much as
       possible like the built-ins "lc" and "uc"; it imposes a scalar context on its argument,
       and if called with no argument it will return the case-folded version of $_.

   case_fold($str)
       Exported on request. Just like "fc", except that it has no prototype and won't case-fold
       $_ if called without an argument.

VARIABLES

   $Unicode::CaseFold::XS
       Whether the XS extension is in use. The pure-perl implementation is 5-10 times slower than
       the XS extension, and on versions of perl before 5.10.0 it will use simple case-folding
       instead of full case-folding (see below).

   $Unicode::CaseFold::SIMPLE_FOLDING
       Is set to true if the perl version is prior to 5.10.0 and the XS extension is not
       available. In this case, "fc" will perform a simple case-folding instead of a full case-
       folding. Although relatively few characters are affected, strings case-folded using simple
       folding might not compare equal to the corresponding strings case-folded with full
       folding, which may cause compatibility issues.

       Furthermore, when simple folding is in use, some strings that would have case-folded to
       the same value when using full folding will instead case-fold to different values. For
       example, "fc("Wei\x{df}")" and "fc("Weiss")" both produce "weiss" when full folding is in
       effect, but the former produces "wei\x{df}" when using simple folding.

       If you want to check for this potentially dangerous situation, consult the
       $Unicode::CaseFold::SIMPLE_FOLDING variable.

COMPATIBILITY

       •   "Unicode::CaseFold" requires Perl 5.8.1 or newer.

       •   Different versions of perl include different versions of the Unicode database, which
           is revised over time. If you are likely to be comparing strings that have been folded
           using different versions of perl, you may need to consult the changes for intervening
           Unicode standard versions to find out whether your code will work correctly.

       •   "Unicode::CaseFold" uses "simple" rather than "full" case-folding when operating in
           Pure-perl mode on perl versions previous to 5.10.0. For compatibility implications,
           see "$Unicode::CaseFold::SIMPLE_FOLDING".

SEE ALSO

       •   <http://unicode.org/reports/tr21/tr21-5.html>: Unicode Standard Annex #21: Case
           Mappings

AUTHOR

       Andrew Rodland <arodland@cpan.org>

COPYRIGHT AND LICENSE

       This software is copyright (c) 2017 by Andrew Rodland.

       This is free software; you can redistribute it and/or modify it under the same terms as
       the Perl 5 programming language system itself.