[swift-corelibs-dev] Bring NSString functions to String

[Andrey Fidrya]

> On 12 May 2017, at 00:05, Tony Parker <anthony.parker at apple.com> wrote:
> 
>> On May 10, 2017, at 4:19 AM, Andrey Fidrya via swift-corelibs-dev <swift-corelibs-dev at swift.org <mailto:swift-corelibs-dev at swift.org>> wrote:
>> 
>> Hi All,
>> 
>> Btw, when migrating from NSString's methods to URL I've noticed
>> that they work a bit differently: URL's methods convert strings
>> from NFC to NFD (decomposed) unicode form which is demonstrated
>> by the example below.
>> 
>> I had to additionally call .precomposedStringWithCanonicalMapping
>> on resulting string to convert it back to NFC form.
>> 
>> This was very surprising as it wasn't mentioned anywhere in docs
>> and has broken non-english filename support in app.
> 
> Out of curiosity, can you explain how this breaks your non-english filename support? What OS and filesystem are you using?

OS X, HFS+. The app reconstructed account names from filenames by dropping file extensions. The filename was converted to NFC form once then NSString's methods were used for manipulating the filename. These methods weren't denormalizing the string. After switching to URL the resulting account names started triggering warnings about invalid characters in them ('й' should have been a valid character, but after denormalizing it was no longer found).

- Andrey

> 
> - Tony
> 
>> Is this expected behavior or a bug?
>> 
>> //let source = "/my_file.txt"
>> let source = "/мой_файл.txt" // problematic is letter 'й'
>> 
>> let disallowedCharacters = CharacterSet(charactersIn: source).inverted
>> 
>> 
>> do {
>>     print("--- NSString:")
>>     let result = (source as NSString).deletingPathExtension as String
>>     print(result)
>>     print(result.rangeOfCharacter(from: disallowedCharacters))
>> 
>> }
>> 
>> do {
>>     print("--- String + URL:")
>>     let result = URL(fileURLWithPath: source).deletingPathExtension().path
>>     print(result)
>>     print(result.rangeOfCharacter(from: disallowedCharacters))
>>     print(result.precomposedStringWithCanonicalMapping.rangeOfCharacter(from: disallowedCharacters))
>> }
>> 
>> 
>> --- Output:
>> 
>> --- NSString:
>> /мой_файл
>> nil
>> --- String + URL:
>> /мой_файл
>> Optional(Range(Swift.String.CharacterView.Index(_base: Swift.String.UnicodeScalarView.Index(_position: 3), _countUTF16: 2)..<Swift.String.CharacterView.Index(_base: Swift.String.UnicodeScalarView.Index(_position: 4), _countUTF16: 1)))
>> nil
>> 
>> 
>> Regards,
>> Andrey
>> 
>>> On 10 May 2017, at 12:45, Eric Blachère via swift-corelibs-dev <swift-corelibs-dev at swift.org <mailto:swift-corelibs-dev at swift.org>> wrote:
>>> 
>>> Thanks for the answer ! It seems a bit weird from them to advocate using NSString methods in the unavailability comment. I would rather use URL when I can even if the conversions are a bit tedious ^^
>>> 
>>> Thanks a lot,
>>> Eric
>>> 
>>> 2017-05-10 10:52 GMT+02:00 Brent Royal-Gordon <brent at architechies.com <mailto:brent at architechies.com>>:
>>> > On May 8, 2017, at 9:39 AM, Eric Blachère via swift-corelibs-dev <swift-corelibs-dev at swift.org <mailto:swift-corelibs-dev at swift.org>> wrote:
>>> >
>>> > I was just wondering if there are plans to bring NSString functions manipulating paths into the native String class. (such as lastPathComponent, pathComponents etc...)
>>> > Because even if we can always make an extension of String to easily cast it into NSString, it's still a bit of a shame to have to do it ;)
>>> 
>>> Unfortunately, it seems like the decision not to include these methods on String was quite deliberate.
>>> 
>>> Here's the revision where that happened: <https://github.com/apple/swift/commit/1f2390f1c75be65f57f189247bfe4f9b2fc11e3b#diff-d38f60064c3752f096c043e756d8f201R925 <https://github.com/apple/swift/commit/1f2390f1c75be65f57f189247bfe4f9b2fc11e3b#diff-d38f60064c3752f096c043e756d8f201R925>> As you can see, they had that working and chose to disable it, presumably because they want you to manipulate paths through `URL`. (I wish the radar referenced in the commit message were public, but alas, it's not.)
>>> 
>>> --
>>> Brent Royal-Gordon
>>> Architechies
>>> 
>>> 
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>> 
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