I wrote a Swift library today for output descriptors. It only has one feature at the moment: calculate the checksum.
Porting the Python checksum code from the Bitcoin Core test suite was fairly easy, except for one thing: Swift is very stubborn about strings, and doesn't believe in character count: "hello" will not compile! I had to jump through a bunch of hoops with ranges. But it works. https://github.com/Sjors/output-descriptors-swift