UNICODE::COLLATE(3perl)

📦
version 5.44.0 · 14 versions
, in arch rolling

okay bestie, sit down, hydrate, because this is Unicode::Collate(3perl) from the Perl Programmers Reference Guide, and it's about to become your entire personality. 💅

✨ NAME ✨

Unicode::Collate — the Unicode Collation Algorithm. That's it, that's the whole thing, that's the legacy. 🌈

🎀 SYNOPSIS 🎀

  use Unicode::Collate;

  #construct
  $Collator = Unicode::Collate->new(%tailoring);

  #sort
  @sorted = $Collator->sort(@not_sorted);

  #compare
  $result = $Collator->cmp($a, $b); # returns 1, 0, or -1.
Note, bestie: the strings sitting in @not_sorted, plus $a and $b, get read according to Perl's Unicode support. Like, go read perlunicode, perluniintro, perlunitut, perlunifaq, utf8. Otherwise you can use "preprocess" or you should decode them before. No skipping that step, fr. 🫶

💖 DESCRIPTION 💖

This module is an implementation of Unicode Technical Standard #10 (a.k.a. UTS #10) — the Unicode Collation Algorithm (a.k.a. UCA). Iconic of it, honestly. 👑

🌸 Constructor and Tailoring 🌸

The "new" method returns a collator object. If new() gets called with no parameters at all, the collator should do the default collation. Cute, low-maintenance, we love.

   $Collator = Unicode::Collate->new(
      UCA_Version => $UCA_Version,
      alternate => $alternate, # alias for 'variable'
      backwards => $levelNumber, # or \@levelNumbers
      entry => $element,
      hangul_terminator => $term_primary_weight,
      highestFFFF => $bool,
      identical => $bool,
      ignoreName => qr/$ignoreName/,
      ignoreChar => qr/$ignoreChar/,
      ignore_level2 => $bool,
      katakana_before_hiragana => $bool,
      level => $collationLevel,
      long_contraction => $bool,
      minimalFFFE => $bool,
      normalization  => $normalization_form,
      overrideCJK => \&overrideCJK,
      overrideHangul => \&overrideHangul,
      preprocess => \&preprocess,
      rearrange => \@charList,
      rewrite => \&rewrite,
      suppress => \@charList,
      table => $filename,
      undefName => qr/$undefName/,
      undefChar => qr/$undefChar/,
      upper_before_lower => $bool,
      variable => $variable,
   );

UCA_Version

If you hand it the revision number of UCA (and yes, back in the day they called this the "tracking version"), it emulates that revision's behavior while collating. If you leave it out, the return value of UCA_Version() gets used instead. The default is 43.

Here's the whole roster of supported revisions, keep it safe:

     UCA       Unicode Standard         DUCET (@version)
   -------------------------------------------------------
      8              3.1                3.0.1 (3.0.1d9)
      9     3.1 with Corrigendum 3      3.1.1
     11             4.0.0
     14             4.1.0
     16             5.0.0
     18             5.1.0
     20             5.2.0
     22             6.0.0
     24             6.1.0
     26             6.2.0
     28             6.3.0
     30             7.0.0
     32             8.0.0
     34             9.0.0
     36            10.0.0
     38            11.0.0
     40            12.0.0
     41            12.1.0
     43            13.0.0
  • See below for "long_contraction" with "UCA_Version" 22 and 24.
  • Noncharacters (e.g. U+FFFF) are not ignored, and can be overridden since "UCA_Version" 22.
  • Out-of-range codepoints (greater than U+10FFFF) are not ignored, and can be overridden since "UCA_Version" 22.
  • Fully ignorable characters were ignored, and would not interrupt contractions with "UCA_Version" 9 and 11.
  • Treatment of ignorables after variables and some behaviors were changed at "UCA_Version" 9.
  • Characters regarded as CJK unified ideographs (cf. "overrideCJK") depend on "UCA_Version".
  • Many hangul jamo are assigned at "UCA_Version" 20, and that will affect "hangul_terminator".

alternate

— see 3.2.2 Alternate Weighting, version 8 of UTS #10.

For backward compatibility, "alternate" (the old name, vintage) can be used as an alias for "variable". 💫

backwards

— see 3.4 Backward Accents, UTS #10.

     backwards => $levelNumber or \@levelNumbers

Weights go in reverse order; e.g. level 2 (diacritic ordering) in French. If you omit it (or $levelNumber is "undef", or "\@levelNumbers" is "[]"), it's forwards at all the levels. Periodt.

entry

— see 5 Tailoring; 9.1 Allkeys File Format, UTS #10.

If the same character (or a sequence of characters) already exists in the collation element table via "table", its mapping to collation elements gets overridden. If it doesn't exist, the mapping is defined additionally. Either way you're making moves. ✨

     entry => <<'ENTRY', # for DUCET v4.0.0 (allkeys-4.0.0.txt)
 0063 0068 ; [.0E6A.0020.0002.0063] # ch
 0043 0068 ; [.0E6A.0020.0007.0043] # Ch
 0043 0048 ; [.0E6A.0020.0008.0043] # CH
 006C 006C ; [.0F4C.0020.0002.006C] # ll
 004C 006C ; [.0F4C.0020.0007.004C] # Ll
 004C 004C ; [.0F4C.0020.0008.004C] # LL
 00F1      ; [.0F7B.0020.0002.00F1] # n-tilde
 006E 0303 ; [.0F7B.0020.0002.00F1] # n-tilde
 00D1      ; [.0F7B.0020.0008.00D1] # N-tilde
 004E 0303 ; [.0F7B.0020.0008.00D1] # N-tilde
 ENTRY
     entry => <<'ENTRY', # for DUCET v4.0.0 (allkeys-4.0.0.txt)
 00E6 ; [.0E33.0020.0002.00E6][.0E8B.0020.0002.00E6] # ae ligature as <a><e>
 00C6 ; [.0E33.0020.0008.00C6][.0E8B.0020.0008.00C6] # AE ligature as <A><E>
 ENTRY
NOTE: the code point in the UCA file format (the bit before the ;) must be a Unicode code point (defined as hexadecimal) — not a native code point. So 0063 must always denote "U+0063", but not a character of "\x63". Do not play yourself here. 💀

Weighting may vary depending on the collation element table. So make sure the weights you define in "entry" are consistent with the ones in the collation element table loaded via "table". Consistency is the whole vibe.

In DUCET v4.0.0, the primary weight of "C" is 0E60 and that of "D" is "0E6D". So setting the primary weight of "CH" to "0E6A" (a value between 0E60 and "0E6D") makes the ordering "C < CH < D". And exactly speaking, DUCET already has some characters sitting between "C" and "D": "small capital C" ("U+1D04") with primary weight 0E64, "c-hook/C-hook" ("U+0188/U+0187") with 0E65, and "c-curl" ("U+0255") with 0E69. So a primary weight of "0E6A" for "CH" puts "CH" ordered between "c-curl" and "D". Look at the precision, we love to see it. 🔥

hangul_terminator

— see 7.1.4 Trailing Weights, UTS #10.

If you give it a true value (non-zero, but it should be positive), it gets added as a terminator primary weight to the end of every standard Hangul syllable. The secondary and any higher weights for the terminator are set to zero. If the value is false, or the "hangul_terminator" key just doesn't exist, then no terminator weights get inserted at all.

Boundaries of Hangul syllables are determined according to conjoining Jamo behavior in the Unicode Standard and HangulSyllableType.txt.

Implementation Note: (1) For expansion mapping (a Unicode character mapped to a sequence of collation elements), a terminator will not be added between collation elements, even if a Hangul syllable boundary exists right there. Addition of the terminator is restricted to the next position to the last collation element.

(2) Non-conjoining Hangul letters (Compatibility Jamo, halfwidth Jamo, and enclosed letters) are not automatically terminated with a terminator primary weight. These characters may need a terminator included in a collation element table beforehand. Noted, bestie. 📝

highestFFFF

— see 2.4 Tailored noncharacter weights, UTS #35 (LDML) Part 5: Collation.

If you make this parameter true, "U+FFFF" gets a highest primary weight. When a boolean of "$coll->ge($str, "abc")" and "$coll->le($str, "abc\x{FFFF}")" is true, it's expected that $str begins with "abc", or another primary equivalent. $str may be "abcd", "abc012", but it should not include "U+FFFF" such as "abc\x{FFFF}xyz".

"$coll->le($str, "abc\x{FFFF}")" works like "$coll->lt($str, "abd")" almost, but the latter has a problem: you should know which letter is next to "c". For a certain language where "ch" is the next letter, "abch" is greater than "abc\x{FFFF}", but less than "abd". Subtle but iconic.

Note: This is equivalent to "(entry => 'FFFF ; [.FFFE.0020.0005.FFFF]')". Any other character than "U+FFFF" can be tailored by "entry".

identical

— see A.3 Deterministic Comparison, UTS #10.

By default, strings whose weights are equal should be equal, even though their code points are not equal. Completely ignorable characters are ignored.

If you make this parameter true, a final, tie-breaking level gets used. If no difference of weights is found after the comparison through all the levels specified by "level", then the comparison with code points will be performed. For the tie-breaking comparison, the sort key has the code points of the original string appended. And completely ignorable characters are not ignored here.

If "preprocess" and/or "normalization" is applied, the code points of the string after them (in NFD by default) are used. 🦋

ignoreChar

ignoreName

— see 3.6 Variable Weighting, UTS #10.

Makes the entry in the table completely ignorable; i.e., as if the weights were zero at all level. Yes, all of them.

Through "ignoreChar", any character matching "qr/$ignoreChar/" will be ignored. Through "ignoreName", any character whose name (given in the "table" file as a comment) matches "qr/$ignoreName/" will be ignored.

E.g. when 'a' and 'e' are ignorable, 'element' is equal to 'lament' (or 'lmnt'). Wild, right? 😭

ignore_level2

— see 5.1 Parametric Tailoring, UTS #10.

By default, case-sensitive comparison (that is a level 3 difference) won't ignore accents (that is a level 2 difference).

If you make this parameter true, accents (and other primary ignorable characters) are ignored, even though cases are taken into account.

NOTE: "level" should be 3 or greater. Don't come crying to me if you set it lower. 🙈

katakana_before_hiragana

— see 7.2 Tertiary Weight Table, UTS #10.

By default, hiragana is before katakana. If you make this parameter true, that gets reversed.

NOTE: This parameter simplemindedly assumes that any hiragana/katakana distinctions must occur in level 3, and that their weights at level 3 must be the same as the ones mentioned in 7.3.1, UTS #10. If you define your own collation elements that violate this requirement, this parameter will not work validly. Fair warning, bestie. ⚠️

level

— see 4.3 Form Sort Key, UTS #10.

Sets the maximum level. Any higher levels than the one you specified are just ignored, bye.

  Level 1: alphabetic ordering
  Level 2: diacritic ordering
  Level 3: case ordering
  Level 4: tie-breaking (e.g. in the case when variable is 'shifted')
             ex.level => 2,

If you don't pass any level at all, the maximum is the 4th. 🎀

⚠️ NOTE, bestie, read this one: the DUCET literally ships weights over 0xFFFF at the 4th level. But this module only ever uses weights within 0xFFFF. So when variable is 'blanked' or 'non-ignorable' — i.e. anything other than 'shifted' and 'shift-trimmed' — the level 4 can be unreliable. Not our fault, it's the table. 😭

See also identical 💖

🌸 long_contraction 🌸

👉 see 3.8.2 Well-Formedness of the DUCET, 4.2 Produce Array, UTS #10.

Set this parameter to a true value and, for a contraction made of three or more characters (we call those "long contraction" around here, it's giving exclusive 💅), the initial substrings get handled properly. So like: contraction ABC, where A is a starter and B and C are non-starters (a character with non-zero combining character class) — it'll be detected even if there's no AB sitting around as a contraction. Iconic.

Default: usually false. But! If UCA_Version is 22 or 24, and you never specified a value for long_contraction in new(), then a true value gets set implicitly. That's a workaround so we can pass the Conformance Tests for Unicode 6.0.0 and 6.1.0. 🫶

change() handles long_contraction explicitly only. So if you don't pass it to change(), then even if UCA_Version changes, long_contraction will not change. no cap.

Limitation: scanning non-starters is one-way (no back tracking 🔙🚫). If AB is found but ABC is not found, other long contractions where the first character is A and the second isn't B may not be found.

Under (normalization => undef), the detection step of discontiguous contractions gets skipped entirely.

Note: these contractions in DUCET are not considered in steps S2.1.1 to S2.1.3, because there they're discontiguous:

0FB2 0F71 0F80 (TIBETAN VOWEL SIGN VOCALIC RR)
0FB3 0F71 0F80 (TIBETAN VOWEL SIGN VOCALIC LL)

For example, TIBETAN VOWEL SIGN VOCALIC RR combined with COMBINING TILDE OVERLAY (U+0344) is 0FB2 0344 0F71 0F80 in NFD. In that case, 0FB2 0F80 (TIBETAN VOWEL SIGN VOCALIC R) is detected instead of 0FB2 0F71 0F80. The inserted 0344 makes 0FB2 0F71 0F80 discontiguous, and the lack of a contraction 0FB2 0F71 forbids 0FB2 0F71 0F80 from ever being detected. rude honestly. 💀

🦋 minimalFFFE 🦋

👉 see 1.1.1 U+FFFE, UTS #35 (LDML) Part 5: Collation.

Make this true and U+FFFE gets a minimal primary weight. Then comparing "$a1\x{FFFE}$a2" against "$b1\x{FFFE}$b2" first compares $a1 and $b1 at level 1, and then $a2 and $b2 at level 1, like so:

"ab\x{FFFE}a"
"Ab\x{FFFE}a"
"ab\x{FFFE}c"
"Ab\x{FFFE}c"
"ab\x{FFFE}xyz"
"abc\x{FFFE}def"
"abc\x{FFFE}xYz"
"aBc\x{FFFE}xyz"
"abcX\x{FFFE}def"
"abcx\x{FFFE}xyz"
"b\x{FFFE}aaa"
"bbb\x{FFFE}a"

Note: this is equivalent to (entry => 'FFFE ; [.0001.0020.0005.FFFE]'). And literally any character other than U+FFFE can be tailored the same way with entry. 💜

🧚 normalization 🧚

👉 see 4.1 Normalize, UTS #10.

Specify this and your strings get normalized before the sort keys are prepared (yes, the normalization runs after preprocess). ✨

Any form name that Unicode::Normalize::normalize() accepts gets applied as $normalization_form. Acceptable names include 'NFD', 'NFC', 'NFKD', and 'NFKC'. Peep Unicode::Normalize::normalize() for the deets. If you omit it, 'NFD' is used.

normalization is performed after preprocess (if it's defined).

Also — two ✨special✨ values, undef and "prenormalized", can be used, even though they've got nothing to do with Unicode::Normalize::normalize().

  • Pass undef (not the string "undef", be so fr) explicitly as the value for this key and no normalization happens at all. That may make tailoring easier if you don't want any normalization. Under (normalization => undef), only contiguous contractions are resolved; e.g. even if "A-ring" (and "A-ring-cedilla") is ordered after "Z", "A-cedilla-ring" would be primary equal to "A". Which means: (normalization => undef, preprocess => sub { NFD(shift) }) is not equivalent to (normalization => 'NFD'). 🚨
  • With (normalization => "prenormalized"), no normalization is performed, but discontiguous contractions with combining characters are. So (normalization => 'prenormalized', preprocess => sub { NFD(shift) }) is equivalent to (normalization => 'NFD'). And if your source strings are already finely prenormalized, (normalization => 'prenormalized') might save you time on normalization. slay, efficiency. ⭐

Except for (normalization => undef), Unicode::Normalize is required (see also CAVEAT later, bestie).

👑 overrideCJK 👑

👉 see 7.1 Derived Collation Elements, UTS #10.

By default, CJK unified ideographs are ordered in Unicode codepoint order — but those in the CJK Unified Ideographs block come in less than those in the CJK Unified Ideographs Extension A etc. Obsessed with consistency.

In the CJK Unified Ideographs block:
U+4E00..U+9FA5 if UCA_Version is 8, 9 or 11.
U+4E00..U+9FBB if UCA_Version is 14 or 16.
U+4E00..U+9FC3 if UCA_Version is 18.
U+4E00..U+9FCB if UCA_Version is 20 or 22.
U+4E00..U+9FCC if UCA_Version is 24 to 30.
U+4E00..U+9FD5 if UCA_Version is 32 or 34.
U+4E00..U+9FEA if UCA_Version is 36.
U+4E00..U+9FEF if UCA_Version is 38, 40 or 41.
U+4E00..U+9FFC if UCA_Version is 43.

In the CJK Unified Ideographs Extension blocks:
Ext.A (U+3400..U+4DB5)   if UCA_Version is  8 to 41.
Ext.A (U+3400..U+4DBF)   if UCA_Version is 43.
Ext.B (U+20000..U+2A6D6) if UCA_Version is  8 to 41.
Ext.B (U+20000..U+2A6DD) if UCA_Version is 43.
Ext.C (U+2A700..U+2B734) if UCA_Version is 20 or later.
Ext.D (U+2B740..U+2B81D) if UCA_Version is 22 or later.
Ext.E (U+2B820..U+2CEA1) if UCA_Version is 32 or later.
Ext.F (U+2CEB0..U+2EBE0) if UCA_Version is 36 or later.
Ext.G (U+30000..U+3134A) if UCA_Version is 43.

Through overrideCJK, the ordering of CJK unified ideographs (extensions included 💅) can be overridden. GIRL you can take the wheel.

ex. CJK unified ideographs in the JIS code point order:

overrideCJK => sub {
    my $u = shift;             # get a Unicode codepoint
    my $b = pack('n', $u);     # to UTF-16BE
    my $s = your_unicode_to_sjis_converter($b); # convert
    my $n = unpack('n', $s);   # convert sjis to short
    [ $n, 0x20, 0x2, $u ];     # return the collation element
},

The return value may be an arrayref of 1st to 4th weights, like above. It may also be an integer, used as the primary weight, like below. And if undef is returned, the default derived collation element gets used instead. 🫶

overrideCJK => sub {
    my $u = shift;             # get a Unicode codepoint
    my $b = pack('n', $u);     # to UTF-16BE
    my $s = your_unicode_to_sjis_converter($b); # convert
    my $n = unpack('n', $s);   # convert sjis to short
    return $n;                 # return the primary weight
},

The return value may also be a list containing zero or more of an arrayref, an integer, or undef.

ex. ignores all CJK unified ideographs:

overrideCJK => sub {()}, # CODEREF returning empty list

 # where ->eq("Pe\x{4E00}rl", "Perl") is true
 # as U+4E00 is a CJK unified ideograph and to be ignorable.

If a false value (including undef) is passed, overrideCJK has no effect. And $Collator->change(overrideCJK => 0) resets the old one back. ctrl+z energy 😌

But — assigning a weight for CJK unified ideographs in table or entry is still valid. If undef is passed explicitly as the value for this key, then weights for CJK unified ideographs are treated as undefined. However, when UCA_Version > 8, (overrideCJK => undef) has no special meaning. periodt.

Note: on top of all that, 12 CJK compatibility ideographs (U+FA0E, U+FA0F, U+FA11, U+FA13, U+FA14, U+FA1F, U+FA21, U+FA23, U+FA24, U+FA27, U+FA28, U+FA29) are also treated as CJK unified ideographs. But they can't be overridden via overrideCJK when you use DUCET, because the table includes weights for them. table or entry has priority over overrideCJK. iykyk 🔥

💜 overrideHangul 💜

👉 see 7.1 Derived Collation Elements, UTS #10.

By default, Hangul syllables get decomposed into Hangul Jamo — even if (normalization => undef). But the mapping of Hangul syllables may be overridden, main character behavior honestly.

This parameter works just like overrideCJK, so go look there for the examples. 👆

If you want to override the mapping of Hangul syllables, NFD and NFKD are not appropriate, since NFD and NFKD will decompose Hangul syllables before the overriding happens. FCD may decompose Hangul syllables as the case may be. 🙈

If a false value (but not undef) is passed, overrideHangul has no effect. $Collator->change(overrideHangul => 0) resets the old one.

If undef is passed explicitly as the value for this key, the weight for Hangul syllables is treated as undefined without decomposition into Hangul Jamo. But defining a weight for Hangul syllables in table or entry is still valid. 💖

🌈 overrideOut 🌈

👉 see 7.1.1 Handling Ill-Formed Code Unit Sequences, UTS #10.

Perl seems to allow out-of-range values (greater than 0x10FFFF). Rude of Perl but okay. By default, out-of-range values get replaced with U+FFFD (REPLACEMENT CHARACTER) when UCA_Version >= 22, or ignored when UCA_Version <= 20.

When UCA_Version >= 22, the weights of out-of-range values can be overridden. table or entry are technically available for them too — but out-of-range values are way too many for that, be so fr.

So overrideOut can do it algorithmically. This parameter works like overrideCJK, so see there for examples. 👆

ex. ignores all out-of-range values:

overrideOut => sub {()}, # CODEREF returning empty list

If a false value (including undef) is passed, overrideOut has no effect. $Collator->change(overrideOut => 0) resets the old one.

🚨 NOTE ABOUT U+FFFD: UCA recommends that out-of-range values should not be ignored, for security reasons. Like, "pe\x{110000}rl" should not be equal to "perl". However — U+FFFD is wrongly mapped to a variable collation element in DUCET for Unicode 6.0.0 to 6.2.0, which means out-of-range values will get ignored when variable isn't Non-ignorable. 💀 a whole security vibe check failing, fr fr.

...and yeah, the mapping of "U+FFFD" got corrected in Unicode 6.3.0, bestie. Peep <http://www.unicode.org/reports/tr10/tr10-28.html#Trailing_Weights> for the receipts — that's 7.1.4 Trailing Weights, and this right here reproduces that whole correction:

overrideOut => sub { 0xFFFD }, # CODEREF returning a very large integer

This workaround is unnecessary since Unicode 6.3.0. like, retired, not coming back, periodt. 💅

preprocess

-- hmm, see 5.4 Preprocessing, UTS #10.

If you specify this, the coderef is used to preprocess every single string before the sort keys get formed. so it's giving prep-work before the glow-up ✨

ex. dropping English articles like "a" or "the". Then "the pen" is before "a pencil".

preprocess => sub {
      my $str = shift;
      $str =~ s/\b(?:an?|the)\s+//gi;
      return $str;
   },

"preprocess" runs before "normalization" (if defined). order matters, no cap.

ex. decoding strings in a legacy encoding such as shift-jis:

$sjis_collator = Unicode::Collate->new(
    preprocess => \&your_shiftjis_to_unicode_decoder,
);
@result = $sjis_collator->sort(@shiftjis_strings);
Note: whatever strings the coderef hands back will be interpreted according to Perl's Unicode support. See perlunicode, perluniintro, perlunitut, perlunifaq, utf8. 🧚

rearrange

-- see 3.5 Rearrangement, UTS #10.

These are characters that aren't coded in logical order and need to be rearranged. If "UCA_Version" is equal to or less than 11, the default is:

rearrange => [ 0x0E40..0x0E44, 0x0EC0..0x0EC4 ],

If you wanna disallow any rearrangement at all, pass undef or [] (a reference to an empty list) as the value for this key.

If "UCA_Version" is equal to or greater than 14, the default is [] (i.e. no rearrangement — chill vibes only).

According to the version 9 of UCA, this parameter shall not be used; but it is not warned at present. 🙈

rewrite

If specified, the coderef is used to rewrite lines in table or entry. The coderef gets each line, and then it should return a rewritten line according to the UCA file format. If the coderef returns an empty line, that line gets skipped. bye bestie 👋

e.g. any primary ignorable characters into tertiary ignorable:

rewrite => sub {
    my $line = shift;
    $line =~ s/\[\.0000\..{4}\..{4}\./[.0000.0000.0000./g;
    return $line;
},

This example is showing off rewriting weights. "rewrite" is allowed to affect code points, weights, and the name. so much power fr fr 👑

NOTE: "table" is available to use another table file; preparing a modified table once would be more efficient than rewriting lines on reading an unmodified table every time. do the work once, live your life.

suppress

-- see 3.12 Special-Purpose Commands, UTS #35 (LDML) Part 5: Collation.

Contractions beginning with the specified characters are suppressed, even if those contractions are defined in "table". gone, not invited. 💀

An example for Russian and some languages using the Cyrillic script:

suppress => [0x0400..0x0417, 0x041A..0x0437, 0x043A..0x045F],

where 0x0400 stands for "U+0400", CYRILLIC CAPITAL LETTER IE WITH GRAVE.

NOTE: Contractions via "entry" will not be suppressed. sneaky little exception.

table

-- see 3.8 Default Unicode Collation Element Table, UTS #10.

You can use another collation element table if you want to, bestie, go off.

The table file should locate in the Unicode/Collate directory on @INC. Say, if the filename is Foo.txt, the table file is searched as Unicode/Collate/Foo.txt in @INC.

By default, allkeys.txt (as the filename of DUCET) is used. If you're gonna prepare your own table file, any name other than allkeys.txt may be better to avoid namespace conflict. don't be messy about it. 💅

NOTE: When XSUB is used, the DUCET is compiled on building this module, and it may save time at the run time. Explicitly saying "(table => 'allkeys.txt')", or using another table, or using "ignoreChar", "ignoreName", "undefChar", "undefName" or "rewrite" will prevent this module from using the compiled DUCET. 😭

If "undef" is passed explicitly as the value for this key, no file is read (but you can define collation elements via "entry"). DIY era.

A typical way to define a collation element table without any file of table:

$onlyABC = Unicode::Collate->new(
    table => undef,
    entry => << 'ENTRIES',
0061 ; [.0101.0020.0002.0061] # LATIN SMALL LETTER A
0041 ; [.0101.0020.0008.0041] # LATIN CAPITAL LETTER A
0062 ; [.0102.0020.0002.0062] # LATIN SMALL LETTER B
0042 ; [.0102.0020.0008.0042] # LATIN CAPITAL LETTER B
0063 ; [.0103.0020.0002.0063] # LATIN SMALL LETTER C
0043 ; [.0103.0020.0008.0043] # LATIN CAPITAL LETTER C
ENTRIES
    );

If "ignoreName" or "undefName" is used, character names should be specified as a comment (following "#") on each line. don't forget the comment or it's not gonna work, iykyk. 🎀

undefChar

undefName

-- see 6.3.3 Reducing the Repertoire, UTS #10.

Undefines the collation element as if it were unassigned in the "table". This reduces the size of the table. If an unassigned character shows up in the string to be collated, the sort key is made from its codepoint as a single-character collation element, as it is greater than any other assigned collation elements (in the codepoint order among the unassigned characters). But, it'd be better to just ignore characters unfamiliar to you that maybe you never even use. selective, iconic. ✨

Through "undefChar", any character matching qr/$undefChar/ will be undefined. Through "undefName", any character whose name (given in the "table" file as a comment) matches qr/$undefName/ will be undefined.

ex. Collation weights for beyond-BMP characters are not stored in object:

undefChar => qr/[^\0-\x{fffd}]/,

upper_before_lower

-- see 6.6 Case Comparisons, UTS #10.

By default, lowercase comes before uppercase. If this parameter is made true, that gets reversed.

NOTE: This parameter simplemindedly assumes that any lowercase/uppercase distinctions must occur in level 3, and their weights at level 3 must be the same as those mentioned in 7.3.1, UTS #10. If you define your collation elements which differs from this requirement, this parameter doesn't work validly. so like... respect the assumption or it won't cooperate. 💀

variable

-- see 3.6 Variable Weighting, UTS #10.

This key allows for variable weighting of variable collation elements, which are marked with an ASTERISK in the table. (NOTE: Many punctuation marks and symbols are variable in allkeys.txt).

variable => 'blanked', 'non-ignorable', 'shifted', or 'shift-trimmed'.

These names are case-insensitive. By default (if the specification is omitted), 'shifted' is adopted. the default is the moment. 👑

  • 'Blanked' — Variable elements are made ignorable at levels 1 through 3; considered at the 4th level.
  • 'Non-Ignorable' — Variable elements are not reset to ignorable.
  • 'Shifted' — Variable elements are made ignorable at levels 1 through 3; their level 4 weight is replaced by the old level 1 weight. Level 4 weight for Non-Variable elements is 0xFFFF.
  • 'Shift-Trimmed' — Same as 'shifted', but all FFFF's at the 4th level are trimmed. ✂️

🎀 Methods for Collation 🎀

"@sorted = $Collator->sort(@not_sorted)"

Sorts a list of strings. that's it, that's the whole job. 💅

"$result = $Collator->cmp($a, $b)"

Returns 1 (when $a is greater than $b) or 0 (when $a is equal to $b) or -1 (when $a is less than $b).

"$result = $Collator->eq($a, $b)"

"$result = $Collator->ne($a, $b)"

"$result = $Collator->lt($a, $b)"

"$result = $Collator->le($a, $b)"

"$result = $Collator->gt($a, $b)"

"$result = $Collator->ge($a, $b)"

They work exactly like the operators with the same names as theirs. sibling energy fr fr 🫶

  • eq : whether $a is equal to $b.
  • ne : whether $a is not equal to $b.
  • lt : whether $a is less than $b.
  • le : whether $a is less than $b or equal to $b.
  • gt : whether $a is greater than $b.
  • ge : whether $a is greater than $b or equal to $b.

"$sortKey = $Collator->getSortKey($string)"

-- see 4.3 Form Sort Key, UTS #10.

Returns a sort key. 🔑

You compare the sort keys using a binary comparison and you get the result of the comparison of the strings using UCA.

$Collator->getSortKey($a) cmp $Collator->getSortKey($b)

   is equivalent to

$Collator->cmp($a, $b)

"$sortKeyForm = $Collator->viewSortKey($string)"

Converts a sorting key into its representation form. If "UCA_Version" is 8, the output is slightly different. (vintage edition ✨)

use Unicode::Collate;
my $c = Unicode::Collate->new();
print $c->viewSortKey("Perl"),"\n";

# output:
# [0B67 0A65 0B7F 0B03 | 0020 0020 0020 0020 | 0008 0002 0002 0002 | FFFF FFFF FFFF FFFF]
#  Level 1               Level 2               Level 3               Level 4

🔍 Methods for Searching 🔍

The "match", "gmatch", "subst", "gsubst" methods work like "m//", "m//g", "s///", "s///g", respectively, but they are not aware of any pattern — only a literal substring. no regex magic here bestie, just vibes.

DISCLAIMER: If "preprocess" or "normalization" parameter is true for $Collator, calling these methods ("index", "match", "gmatch", "subst", "gsubst") is croaked, as the position and the length might differ from those on the specified string. it will genuinely yell at you. 😭

"rearrange" and "hangul_terminator" parameters are neglected. "katakana_before_hiragana" and "upper_before_lower" don't affect matching and searching, as it doesn't matter whether greater or less. they're sitting this one out. 💅

"$position = $Collator->index($string, $substring[, $position])"

"($position, $length) = $Collator->index($string, $substring[, $position])"

If $substring matches a part of $string, returns the position of the first occurrence of the matching part in scalar context; in list context, returns a two-element list of the position and the length of the matching part. 📍

If $substring does not match any part of $string, returns -1 in scalar context and an empty list in list context. ghosted. 👻

e.g. when the content of $str is "Ich muß studieren Perl.", you say the following where $sub is "MüSS",

my $Collator = Unicode::Collate->new( normalization => undef, level => 1 );
                                   # (normalization => undef) is REQUIRED.
my $match;
if (my($pos,$len) = $Collator->index($str, $sub)) {
    $match = substr($str, $pos, $len);
}

and get "muß" in $match, since "muß" is primary equal to "MüSS". slay. 🦋🌸

  • $match_ref = $Collator->match($string, $substring)
  • ($match) = $Collator->match($string, $substring)

If $substring matches a part of $string, then in scalar context it hands you back a reference to the first occurrence of the matching part ($match_ref is always true when there's a match, because every reference is true, bestie — that's just how refs work 💅). In list context, it gives you the first occurrence of the matching part itself.

If $substring does not match any part of $string, you get undef in scalar context and an empty list in list context. Rude? a little. Correct? completely. 🙈

e.g.

if ($match_ref = $Collator->match($str, $sub)) { # scalar context
    print "matches [$$match_ref].\n";
} else {
    print "doesn't match.\n";
}

or

if (($match) = $Collator->match($str, $sub)) { # list context
    print "matches [$match].\n";
} else {
    print "doesn't match.\n";
}
  • @match = $Collator->gmatch($string, $substring)

If $substring matches a part of $string, this returns all the matching parts — or, in scalar context, the matching count. (The g is for "global", iykyk 😌)

If $substring doesn't match any part of $string, you get an empty list.

  • $count = $Collator->subst($string, $substring, $replacement)

If $substring matches a part of $string, the first occurrence of the matching part gets replaced by $replacement ($string is modified, like for real mutated 💀) and $count is returned — always equals to 1.

$replacement can be a CODEREF, taking the matching part as an argument and returning a string to replace the matching part (a bit similar to s/(..)/$coderef->($1)/e).

  • $count = $Collator->gsubst($string, $substring, $replacement)

If $substring matches a part of $string, all the occurrences of the matching part are replaced by $replacement ($string is modified) and $count is returned.

$replacement can be a CODEREF, taking the matching part as an argument and returning a string to replace the matching part (a bit similar to s/(..)/$coderef->($1)/eg).

e.g.

my $Collator = Unicode::Collate->new( normalization => undef, level => 1 );
                                   # (normalization => undef) is REQUIRED.
my $str = "Camel donkey zebra came\x{301}l CAMEL horse cam\0e\0l...";
$Collator->gsubst($str, "camel", sub { "<b>$_[0]</b>" });

# now $str is "<b>Camel</b> donkey zebra <b>came\x{301}l</b> <b>CAMEL</b> horse <b>cam\0e\0l</b>...";
# i.e., all the camels are made bold-faced.
 Examples: levels and ignore_level2 - what does camel match?
---------------------------------------------------------------------------
 level  ignore_level2  |  camel  Camel  came\x{301}l  c-a-m-e-l  cam\0e\0l
-----------------------|---------------------------------------------------
   1        false      |   yes    yes      yes          yes        yes
   2        false      |   yes    yes      no           yes        yes
   3        false      |   yes    no       no           yes        yes
   4        false      |   yes    no       no           no         yes
-----------------------|---------------------------------------------------
   1        true       |   yes    yes      yes          yes        yes
   2        true       |   yes    yes      yes          yes        yes
   3        true       |   yes    no       yes          yes        yes
   4        true       |   yes    no       yes          no         yes
---------------------------------------------------------------------------
 note: if variable => non-ignorable, camel doesn't match c-a-m-e-l
       at any level.
ok so the camel table is lowkey sending me but it's literally just: different levels and ignore_level2 change which spellings of "camel" count as a match. Study it, don't fight it 🐪✨

🎀 Other Methods 🎀

  • %old_tailoring = $Collator->change(%new_tailoring)
  • $modified_collator = $Collator->change(%new_tailoring)

Changes the value of specified keys and returns the changed part. Glow-up for your collator, basically 🦋

$Collator = Unicode::Collate->new(level => 4);

$Collator->eq("perl", "PERL"); # false

%old = $Collator->change(level => 2); # returns (level => 4).

$Collator->eq("perl", "PERL"); # true

$Collator->change(%old); # returns (level => 2).

$Collator->eq("perl", "PERL"); # false

Not all (key,value)s are allowed to be changed. See also @Unicode::Collate::ChangeOK and @Unicode::Collate::ChangeNG.

In the scalar context, returns the modified collator (but it is not a clone from the original).

$Collator->change(level => 2)->eq("perl", "PERL"); # true

$Collator->eq("perl", "PERL"); # true; now max level is 2nd.

$Collator->change(level => 4)->eq("perl", "PERL"); # false
  • $version = $Collator->version()

Returns the version number (a string) of the Unicode Standard which the table file used by the collator object is based on. If the table does not include a version line (starting with @version), returns unknown. 😭 it really said "idk her".

  • UCA_Version()

Returns the revision number of UTS #10 this module consults, that should correspond with the DUCET incorporated.

  • Base_Unicode_Version()

Returns the version number of UTS #10 this module consults, that should correspond with the DUCET incorporated.

✨ EXPORT ✨

No method will be exported. Not one. Zero. None. Keep your namespace cute and uncluttered 💅

💾 INSTALL 💾

Though this module can be used without any table file, to use this module easily, it is recommended to install a table file in the UCA format, by copying it under the directory <a place in @INC>/Unicode/Collate.

The most preferable one is The Default Unicode Collation Element Table (aka DUCET), available from the Unicode Consortium's website:

http://www.unicode.org/Public/UCA/

http://www.unicode.org/Public/UCA/latest/allkeys.txt
(latest version)

If DUCET is not installed, it is recommended to copy the file from http://www.unicode.org/Public/UCA/latest/allkeys.txt to <a place in @INC>/Unicode/Collate/allkeys.txt manually. Yes bestie, manually. With your own two hands. 🫶

⚠️ CAVEATS ⚠️

Normalization

Use of the normalization parameter requires the Unicode::Normalize module (see Unicode::Normalize).

If you need not it (say, in the case when you need not handle any combining characters), assign (normalization => undef) explicitly.

-- see 6.5 Avoiding Normalization, UTS #10.

Conformance Test

The Conformance Test for the UCA is available under <http://www.unicode.org/Public/UCA/>.

For CollationTest_SHIFTED.txt, a collator via Unicode::Collate->new( ) should be used; for CollationTest_NON_IGNORABLE.txt, a collator via Unicode::Collate->new(variable => "non-ignorable", level => 3).

If UCA_Version is 26 or later, the identical level is preferred; Unicode::Collate->new(identical => 1) and Unicode::Collate->new(identical => 1, variable => "non-ignorable", level => 3) should be used.

Unicode::Normalize is required to try The Conformance Test.

EBCDIC-SUPPORT IS EXPERIMENTAL. 🔥 like, it's out here living its experimental life, use accordingly.

The Unicode::Collate module for perl was written by SADAHIRO Tomoyuki, <SADAHIRO@cpan.org>. This module is Copyright(C) 2001-2021, SADAHIRO Tomoyuki. Japan. All rights reserved.

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

The file Unicode/Collate/allkeys.txt was copied verbatim from <http://www.unicode.org/Public/UCA/13.0.0/allkeys.txt>. For this file, Copyright (c) 2020 Unicode, Inc.; distributed under the Terms of Use in <http://www.unicode.org/terms_of_use.html>

🔗 SEE ALSO 🔗

<http://www.unicode.org/Public/UCA/latest/CollationTest.zip>

and that's the whole page, bestie!! 🎉 you just read Unicode::Collate(3perl), and this lil guy shipped as part of perl v5.44.0, dated 2026-10-17. go sort some strings in a way that's culturally and linguistically correct, you absolute icon 💖✨🎀🦋

📦 where this page comes from