range function and crash in swift 3 - swift

Question

My below code crashes:
func getrange(_ from: Int, length: Int) -> Range<String.Index>? {
guard let fromU16 = utf16.index(utf16.startIndex, offsetBy: from, limitedBy: utf16.endIndex), fromU16 != utf16.endIndex else {
return nil ----->crashes here
}
let toU16 = utf16.index(fromU16, offsetBy: length, limitedBy: utf16.endIndex) ?? utf16.endIndex
guard let from = String.Index(fromU16, within: self),
let to = String.Index(toU16, within: self) else { return nil }
return from ..< to
}
This code is crashing with swift 3 migration.
Can someone help debugging the issue.
Below is the sequence of events:
//input for below function is: text “123456789”, string “0”, nsrange = location =9, length=0
1) function 1
static func numericText(_ text: String, replacedBy string: String, in nsrange: NSRange) -> String {
guard let range = text.range(for: nsrange) else {
//assertionFailure("Should never reach here")
return text.numericString()
}
// Apply Replacement String to the textField text and extract only the numeric values
return text.replacingCharacters(in: range, with: string)
.numericString()
}
2) function 2
func range(for nsrange: NSRange) -> Range<String.Index>? {
return range(nsrange.location, length: nsrange.length)
}
3) function 3
func range(_ from: Int, length: Int) -> Range<String.Index>? {
guard let fromU16 = utf16.index(utf16.startIndex, offsetBy: from, limitedBy: utf16.endIndex), fromU16 != utf16.endIndex else {
return nil
}
let toU16 = utf16.index(fromU16, offsetBy: length, limitedBy: utf16.endIndex) ?? utf16.endIndex
guard let from = String.Index(fromU16, within: self),
let to = String.Index(toU16, within: self) else { return nil }
return from ..< to
}

Answer 1

Sorry, I didn't update during the weekend.
I reviewed your question.
I can implement your function 1:
extension String {
func getrange(_ from: Int, length: Int) -> Range<String.Index>? {
guard let fromU16 = utf16.index(utf16.startIndex, offsetBy: from, limitedBy: utf16.endIndex), fromU16 != utf16.endIndex else {
return nil
}
let toU16 = utf16.index(fromU16, offsetBy: length, limitedBy: utf16.endIndex) ?? utf16.endIndex
guard let from = String.Index(fromU16, within: self),
let to = String.Index(toU16, within: self) else { return nil }
return from ..< to
}
}
But I cant implement your function 2, is that converted to Swift3 syntax yet?
My question is this,
Below is the sequence of events:
//input for below function is: text “123456789”, string “0”, nsrange = location =9, length=0
your input, your location shouldn't be 9. As your string length is 9, the max location your can replace should be 8?

Answer 2

Just replacing utf with unicodeScalars in the code fixed the issue.