[swift-evolution] Swift String problem with Thai language

[Pitiphong Phongpattranont]

Hello Swift Community,

I’ve found a problem on Swift String API with Thai language. In Thai, we have 44 Consonants, 32 vowels and 5 tone marks. A special attribute of Thai vowels is that they can be put on anywhere around a consonant, some of them are placed after a consonant (ชา), some are before (แช), some are above (ชี) and some are below (ชุ). Since all vowels must be placed along with a consonants but they’re place in difference places around a consonant, Unicode standard says that some of the Thai vowels are Grapheme Base and some are Grapheme Extend.

And because Swift String is fully Unicode compliance and by having some vowels be a Grapheme Extend makes some Thai vowels have a invalid attributes in some aspects. For example a word “ชี” (a nun) and “ชา” (tea) both have one consonant (in this case is ช) and one vowel (ี and า). When we ask how many characters are there in those words or does this word contain a ช character, we should get the same results from those 2 words (2 characters and it contains ช). However I found that in Swift String API, I will get a difference answers from those questions.


// You can try this code snippet in a Swift Playground
let chi = "ชี"
let cha = “ชา"

// Value of these 2 lines below should be 2
chi.characters.count
cha.characters.count

// Value of these 3 lines below should be true
chi.contains("ช")
cha.contains("ช")
chi.characters.contains("ช”)

// end of code snippet


I’m not sure that if Swift team is aware of this problem and do they have any opinion on it. I know that Unicode is very very hard and do aware of that there would be a revamp on String API in Swift 4 so I want to make this into a discussion before Swift 4 is released.


Thank you,
Bank (Pitiphong)