117 lines
3.1 KiB
Plaintext
117 lines
3.1 KiB
Plaintext
== Case Mapping
|
||
|
||
Some string-oriented methods use case mapping.
|
||
|
||
In String:
|
||
|
||
- String#capitalize
|
||
- String#capitalize!
|
||
- String#casecmp
|
||
- String#casecmp?
|
||
- String#downcase
|
||
- String#downcase!
|
||
- String#swapcase
|
||
- String#swapcase!
|
||
- String#upcase
|
||
- String#upcase!
|
||
|
||
In Symbol:
|
||
|
||
- Symbol#capitalize
|
||
- Symbol#casecmp
|
||
- Symbol#casecmp?
|
||
- Symbol#downcase
|
||
- Symbol#swapcase
|
||
- Symbol#upcase
|
||
|
||
=== Default Case Mapping
|
||
|
||
By default, all of these methods use full Unicode case mapping,
|
||
which is suitable for most languages.
|
||
See {Unicode Latin Case Chart}[https://www.unicode.org/charts/case].
|
||
|
||
Non-ASCII case mapping and folding are supported for UTF-8,
|
||
UTF-16BE/LE, UTF-32BE/LE, and ISO-8859-1~16 Strings/Symbols.
|
||
|
||
Context-dependent case mapping as described in
|
||
{Table 3-17 of the Unicode standard}[https://www.unicode.org/versions/Unicode13.0.0/ch03.pdf]
|
||
is currently not supported.
|
||
|
||
In most cases, case conversions of a string have the same number of characters.
|
||
There are exceptions (see also +:fold+ below):
|
||
|
||
s = "\u00DF" # => "ß"
|
||
s.upcase # => "SS"
|
||
s = "\u0149" # => "ʼn"
|
||
s.upcase # => "ʼN"
|
||
|
||
Case mapping may also depend on locale (see also +:turkic+ below):
|
||
|
||
s = "\u0049" # => "I"
|
||
s.downcase # => "i" # Dot above.
|
||
s.downcase(:turkic) # => "ı" # No dot above.
|
||
|
||
Case changes may not be reversible:
|
||
|
||
s = 'Hello World!' # => "Hello World!"
|
||
s.downcase # => "hello world!"
|
||
s.downcase.upcase # => "HELLO WORLD!" # Different from original s.
|
||
|
||
Case changing methods may not maintain Unicode normalization.
|
||
See String#unicode_normalize).
|
||
|
||
=== Options for Case Mapping
|
||
|
||
Except for +casecmp+ and +casecmp?+,
|
||
each of the case-mapping methods listed above
|
||
accepts optional arguments, <tt>*options</tt>.
|
||
|
||
The arguments may be:
|
||
|
||
- +:ascii+ only.
|
||
- +:fold+ only.
|
||
- +:turkic+ or +:lithuanian+ or both.
|
||
|
||
The options:
|
||
|
||
- +:ascii+:
|
||
ASCII-only mapping:
|
||
uppercase letters ('A'..'Z') are mapped to lowercase letters ('a'..'z);
|
||
other characters are not changed
|
||
|
||
s = "Foo \u00D8 \u00F8 Bar" # => "Foo Ø ø Bar"
|
||
s.upcase # => "FOO Ø Ø BAR"
|
||
s.downcase # => "foo ø ø bar"
|
||
s.upcase(:ascii) # => "FOO Ø ø BAR"
|
||
s.downcase(:ascii) # => "foo Ø ø bar"
|
||
|
||
- +:turkic+:
|
||
Full Unicode case mapping, adapted for the Turkic languages
|
||
that distinguish dotted and dotless I, for example Turkish and Azeri.
|
||
|
||
s = 'Türkiye' # => "Türkiye"
|
||
s.upcase # => "TÜRKIYE"
|
||
s.upcase(:turkic) # => "TÜRKİYE" # Dot above.
|
||
|
||
s = 'TÜRKIYE' # => "TÜRKIYE"
|
||
s.downcase # => "türkiye"
|
||
s.downcase(:turkic) # => "türkıye" # No dot above.
|
||
|
||
- +:lithuanian+:
|
||
Not yet implemented.
|
||
|
||
- +:fold+ (available only for String#downcase, String#downcase!,
|
||
and Symbol#downcase):
|
||
Unicode case folding,
|
||
which is more far-reaching than Unicode case mapping.
|
||
|
||
s = "\u00DF" # => "ß"
|
||
s.downcase # => "ß"
|
||
s.downcase(:fold) # => "ss"
|
||
s.upcase # => "SS"
|
||
|
||
s = "\uFB04" # => "ffl"
|
||
s.downcase # => "ffl"
|
||
s.upcase # => "FFL"
|
||
s.downcase(:fold) # => "ffl"
|