With the Swift 5 compiler changing
String's native representation to be backed by UTF-8, code that wants to operate as fast as possible on
String code units should naturally use UTF-8. However if the
String is bridged from
NSString then the backing representation will still be UTF-16.
Is there any supported way to detect if a given
String is backed by UTF-8 or UTF-16, so I can pick the appropriate implementation?
I think the property you're looking for is referred to inside the stdlib via "_guts.isFastUTF8". I'm not sure if that's currently exposed in the API though.
Looking at the Swift 5 stdlib right now I see a method
withContiguousStorageIfAvailable(_:) that seems to do that test, but it's completely undocumented and I don't know if it's appropriate to use for this case.
That looks like precisely what I want. Thanks!
Also it does confirm that
withContiguousStorageIfAvailable can be used for the test right now, although kind of awkwardly.