Попробуйте это для простого решения Swift 4
extension String {
func stripExtension(_ extensionSeperator: Character = ".") -> String {
let selfReversed = self.reversed()
guard let extensionPosition = selfReversed.index(of: extensionSeperator) else { return self }
return String(self[..<self.index(before: (extensionPosition.base.samePosition(in: self)!))])
}
}
print("hello.there.world".stripExtension())
// prints "hello.there"