Feature #10002: String swapcase

• Status: Closed
• Assignee: -
• Target version: -

[randy15 (Andreas Runk)]

Hi, the ruby version 2.1.2 has a problem with the .swapcase function and german letters.
E.g. "ä".swapcase does return "ä" but should be "Ä".

[nobu (Nobuyoshi Nakada)]

• Tracker changed from Bug to Feature

[matz (Yukihiro Matsumoto)]

The current implementation of case conversion methods in String class only understands ASCII characters.
We'd like to enhance it when possible. But we have to know how each character should be converted.
For example, how should we convert "ß" (eszett)?

Matz.

[naruse (Yui NARUSE)]

At this time, ffi-icu or twitter-text-rb is useful.

[davispuh (Dāvis Mosāns)]

It have been already figured out by Unicode Standard, so just have to implement it. Look at Default Case Algorithms in section 3.13 and Case Mappings in section 5.18. Mappings can be viewed in SpecialCasing.txt (and UnicodeData.txt) also CaseFolding.txt could be useful.

From there "ß" (LATIN SMALL LETTER SHARP S) in uppercase would be "SS" (LATIN CAPITAL LETTER S) and it's user's responsibility to know that generally they are not reversible.

Also useful to read Character Properties, Case Mappings & Names FAQ

[zzak (zzak _)]

We should delegate to @emboss everytime we need to convert ß...

[shyouhei (Shyouhei Urabe)]

We are talking about swapcase, not folding. The "generally they are not reversible" you say is the difficulty we are facing here. Also as you cited CaseFolding.txt, you should have been aware of type T folding, which is impossible without locale information.

If you think you can implement it, please show us.

Dāvis Mosāns wrote:

It have been already figured out by Unicode Standard, so just have to implement it. Look at Default Case Algorithms in section 3.13 and Case Mappings in section 5.18. Mappings can be viewed in SpecialCasing.txt (and UnicodeData.txt) also CaseFolding.txt could be useful.

From there "ß" (LATIN SMALL LETTER SHARP S) in uppercase would be "SS" (LATIN CAPITAL LETTER S) and it's user's responsibility to know that generally they are not reversible.

Also useful to read Character Properties, Case Mappings & Names FAQ

[duerst (Martin Dürst)]

• Related to Feature #10085: Add non-ASCII case conversion to String#upcase/downcase/swapcase/capitalize added

[duerst (Martin Dürst)]

• Status changed from Open to Closed

This has actually been implemented by Feature #10085, so it can be closed.