Swift CharacterSet减法

为什么characters1不为空？

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

一切都好

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

解决方法

从 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语脚本(和其他脚本)的数字.