Only 2 emoji return incorrect length when compared to a character set containing them

let myString = "☺️"

let emoji = "😀😁😂😃😄😅😆😇😈👿😉😊☺️😋😌😍😎😏😐😑😒😓😔😕😖😗😘😙😚😛😜😝😞😟😠😡😢😣😤😥😦😧😨😩😪😫😬😭😮😯😰😱😲😳😴😵😶😷🙂🙃🙄🤔🙁☹️🤒🤕🤑🤓🤗🤐🤠🤤🤥🤧🤢🤡🤣"

let characterSet = CharacterSet(charactersIn: emoji)

let range = (myString as NSString).rangeOfCharacter(from: characterSet)
(myString as NSString).substring(with: range)
(range as NSRange).location
(range as NSRange).length
(myString as NSString).length

substring == myString

      

        
        
        
      

    

This code can be run on playgrounds. Try changing myString to any emotion face.

I am using NSString and NSRange here as their values ​​are easier to demonstrate, but it has the same behavior with Swift String or Range.

When I set myString for most of the emojis face, the range is returned as having a length of 2, and the substring can be used appropriately elsewhere. Only 2 faces emojis - smiling face "emoji" and " frowning face " emoji, the range is returned as length 1. In all cases, the length of the string is returned as 2. The substring with the given range of 1 is incomplete and you can see the comparison it goes back to myString as an example comparing it to itself yields false The result for the range of these 2 emojis should be 2.

Interestingly, looking at the unicode spec, these 2 emojis have significantly different unicode values ​​for their neighbors.

It seems like it might be an iOS bug. I can't think of anything I could personally do wrong here as it works with all other emojis.