Getting a empty Range<String.Index> in Swift - swift

Question

I am very new to Swift and have trying to use regular expressions, but getting the match from the string seems to be an insurmountable task.
This is my current approach.
print(data.substring(with: (data.range(of: "[a-zA-Z]at", options: .regularExpression))))
This doesn't work because
Value of optional type 'Range<String.Index>?' must be unwrapped to a value of type 'Range<String.Index>'
I guess this has something to do with it possibly being null, so now i want to provide it with an alternative using the ?? operator.
print(data.substring(with: (data.range(of: "[a-zA-Z]at", options: .regularExpression) ?? Range<String.Index>())))
What i want to do is to provide it with an empty range object but it seems to be impossible to create an empty object of the type required.
Any suggestions?

Answer 1

There is simply no argument-less initialiser for Range<String.Index>.
One way you can create an empty range of String.Index is to use:
data.startIndex..<data.startIndex
Remember that you shouldn't use integers here, because we are dealing with indices of a string. See this if you don't understand why.
So:
print(data.substring(with: (data.range(of: "[a-zA-Z]at", options: .regularExpression) ?? data.startIndex..<data.startIndex)))
But substring(with:) is deprecated. You are recommended to use the subscript:
print(data[data.range(of: "[a-zA-Z]at", options: .regularExpression) ?? data.startIndex..<data.startIndex])

Answer 2

Instead of trying to create an empty range, I would suggest creating an empty Substring in case there was no match. Range can be quite error-prone, so using this approach you can save yourself a lot of headaches.
let match: Substring
if let range = data.range(of: "[a-zA-Z]at", options: .regularExpression) {
match = data[range]
} else {
match = ""
}
print(match)

Answer 3

You can create such constructor with a simple extension to Range type. Like this:
extension Range where Bound == String.Index {
static var empty: Range<Bound> {
"".startIndex..<"".startIndex
}
init() {
self = Range<Bound>.empty
}
}
Then it can be used like this:
let str = "kukukukuku"
let substr1 = str[str.range(of: "abc", options: .regularExpression) ?? Range<String.Index>()]
let substr2 = str[str.range(of: "abc", options: .regularExpression) ?? Range<String.Index>.empty]