Method: UnicodeUtils.downcase

Defined in:
lib/unicode_utils/downcase.rb

.downcase(str, language_id = nil) ⇒ Object

Perform a full case-conversion of str to lowercase according to the Unicode standard.

Some conversion rules are language dependent, these are in effect when a non-nil language_id is given. If non-nil, the language_id must be a two letter language code as defined in BCP 47 (tools.ietf.org/rfc/bcp/bcp47.txt) as a symbol. If a language doesn't have a two letter code, the three letter code is to be used. If locale independent behaviour is required, nil should be passed explicitely, because a later version of UnicodeUtils may default to something else.

Examples:

require "unicode_utils/downcase"
UnicodeUtils.downcase("") => ""
UnicodeUtils.downcase("aBI\u{307}", :tr) => "abi"

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# File 'lib/unicode_utils/downcase.rb', line 28

def downcase(str, language_id = nil)
  String.new.force_encoding(str.encoding).tap { |res|
    if Impl::LANGS_WITH_RULES.include?(language_id)
      # ensure O(1) lookup by index
      str = str.encode(Encoding::UTF_32LE)
    end
    pos = 0
    str.each_codepoint { |cp|
      special_mapping =
        Impl.conditional_downcase_mapping(cp, str, pos, language_id) ||
        SPECIAL_DOWNCASE_MAP[cp]
      if special_mapping
        special_mapping.each { |m| res << m }
      else
        res << (SIMPLE_DOWNCASE_MAP[cp] || cp)
      end
      pos += 1
    }
  }
end