Meziantou.Framework

Case conversion

edit

Convert a text

UnicodeCaseMapping.ToUpper and ToLower convert a whole text with the full case mappings of the standard, a character being able to become several ones:

// The mappings that do not depend on the language, with the final sigma of Greek
Assert.Equal("STRASSE", UnicodeCaseMapping.ToUpper("Stra\u00DFe"));
Assert.Equal("\u03BF\u03B4\u03CC\u03C2", UnicodeCaseMapping.ToLower("\u039F\u0394\u038C\u03A3"));

// Turkish and Azerbaijani: the dotless and the dotted I
Assert.Equal("\u0131i", UnicodeCaseMapping.ToLower("I\u0130", "tr"));
Assert.Equal("\u0130I", UnicodeCaseMapping.ToUpper("i\u0131", "tr-TR"));

// Lithuanian: the i keeps its dot under an accent
Assert.Equal("i\u0307\u0300", UnicodeCaseMapping.ToLower("\u00CC", "lt"));
  • The second parameter is the language of the text, as a BCP 47 language tag (tr, lt-LT); only the language subtag is read, ignoring case. null selects the mappings that do not depend on the language.
  • In every language, a Greek capital sigma becomes the final sigma at the end of a word, and the small sigma elsewhere.
  • In Turkish and Azerbaijani (tr, az), I and i are distinct letters from the dotless ı and the dotted İ.
  • In Lithuanian (lt), a lowercase i keeps its dot under an accent.
  • The other languages have no rule of their own in the standard: they use the mappings that do not depend on the language.

Why not string.ToUpper

string.ToUpper(CultureInfo) depends on the globalization library of the operating system and on its version. UnicodeCaseMapping does not: it gives the same result on every platform and every version of .NET, including in globalization-invariant mode, for the version of Unicode of the package. An unpaired surrogate is copied as it is.

The rules of the Common Locale Data Repository that the standard does not include, such as removing the accents of Greek when uppercasing, are not applied.

Compare without case

To compare two texts without case, do not convert both to lowercase: case folding is made for comparison. Fold each code point with UnicodeProperties.ToSimpleCaseFold, after normalizing the texts. See Character properties.