Swift 字符集减法

Question

为什么characters1不为空？

var characters1 = CharacterSet.decimalDigits
let characters2 = CharacterSet(charactersIn: "01234567890")
characters1.subtract(characters2)
print(characters1.isEmpty)

这里一切正常

var characters1 = CharacterSet(charactersIn: "9876543210")
let characters2 = CharacterSet(charactersIn: "0123456789")
characters1.subtract(characters2)
print(characters1.isEmpty)

Answer 1

来自docs (强调我的)

Informally, this set is the set of all characters used to represent the decimal values 0 through 9. These characters include, for example, the decimal digits of the Indic scripts and Arabic.

因此，CharacterSet.decimalDigits 不仅包含“9876543210”，它们还包含来自印度文字(和其他文字)的数字。