CC @milseman

Comment by Kyle Macomber (JIRA)

@swift-ci create

This behaves correctly – String and NSString operate on different levels of abstraction. NSString counts UTF-16 code units, while String counts Unicode grapheme clusters (which are closer to what people typically consider "characters").

For example, the character "क्" from the beginning of the Hindi example is actually composed of two Unicode scalars, but it's still considered a single character.

"क" – U+0915 DEVANAGARI LETTER KA
"्" – U+094D DEVANAGARI SIGN VIRAMA

NSString and NSAttributedString considers "क्" a string of length 2, while String has its count as 1. Neither of these is incorrect – the correct answer depends on what we mean by "character", which changes from problem to problem. While processing text, you need to always keep in mind what representation you're working with, especially while interfacing with libraries not written in Swift, like Cocoa here.

To interface with NSAttributedString indices, you'll need to use the `.utf16` view on String:

let hindi = "क्या आप Chat पर नए हैं?"
print(hindi.count)  // ⟹ 19
print(hindi.utf16.count) // ⟹ 23
print((hindi as NSString).length) // ⟹ 23

let thai = "เพิ่งเริ่มแชทใช่หรอไม่"
print(thai.count) // ⟹ 16
print(thai.utf16.count) // ⟹ 22
print((thai as NSString).length) // ⟹ 22

Besides `.utf16`, String also provides `.utf8` and `.unicodeScalars` views that provide additional ways to count String contents:

"�‍♂️".count // ⟹ 1

"�‍♂️".unicodeScalars.count // ⟹ 4

"�‍♂️".utf16.count // ⟹ 5

"�‍♂️".utf8.count // ⟹ 13

("�‍♂️" as NSString).length // ⟹ 5 (same as .utf16)

From the String documentation:

For more details, see the rest of the Swift documentation (and, ultimately, the Unicode standard).

Jira's dodgy Unicode support failed me there. The last examples were supposed to include the hugely useful "dancing men wearing bunny ears" emoji, represented by the single-character string "\u{1F46F}\u{200D}\u{2642}\u{FE0F}".