[SR-3597] CharacterSet isEmpty method failing

[swift-ci]

Previous ID	SR-3597
Radar	None
Original Reporter	Nteissler (JIRA User)
Type	Bug

Attachment: Download

Additional Detail from JIRA

Votes	0
Component/s
Labels	Bug, CharacterSet
Assignee	None
Priority	Medium

md5: 27b6a52ddd0420df6cf1819fe7ce0c67

Issue Description:

I was trying to user CharacterSet to check if a user input string contains any non decimal digit characters. I use CharacterSet.decimalDigits and take the intersection of that with the user input. If this intersection is empty, it presumably means the user hasn't entered valid input. Yet the intersection is not empty.

let digits = CharacterSet.decimalDigits  
let letters = CharacterSet(charactersIn: "abcd") // never prints

let intersection = digits.intersection(letters)  
for c in "abcd".characters {  
  if intersection.contains(UnicodeScalar(String(c))!) {  
    print("contains \(c)") // never prints  
  }  
}

for i in 0...9 {  
  if intersection.contains(UnicodeScalar(String(i))!) {  
    print("contains \(i)")  
  }  
}

print("intersection is empty: (intersection.isEmpty)") // prints false

I even tried looping over all unicode scalars to test for membership, and that doesn't print anything.

for i in 0x0000...0xFFFF {  
  guard let c = UnicodeScalar(i) else {  
    continue  
  }  
  if intersection.contains(c) {  
    print("contains \(c)")  
  }  
}

Why is the set non empty?

Note: using let digits = CharacterSet(charactersIn: "1234567890") works as expected. I know that the decimalDigits contains more than just 0-9, but the intersection should still be empty.

[xwu]

let digits = CharacterSet.decimalDigits  
print(digits.intersection(digits.inverted).isEmpty) // false  
print(digits.intersection(digits.inverted) == digits.inverted.intersection(digits)) // false  

Oops...

[AnthonyLatsis]

@parkera I know this is an old bug that might very well be fixed, but still, could we relocate it to one of the Foundation repositories for triage?