Swift: How to get substring from start to last index of character

Question

I want to learn the best/simplest way to turn a string into another string but with only a subset, starting at the beginning and going to the last index of a character.

Answer 1

The one thing that adds clatter is the repeated stringVar:

stringVar[stringVar.index(stringVar.startIndex, offsetBy: ...)

In Swift 4

An extension can reduce some of that:

extension String {

    func index(at location: Int) -> String.Index {
        return self.index(self.startIndex, offsetBy: location)
    }
}

Then, usage:

let string = "abcde"

let to = string[..

It should be noted that to and from are type Substring (or String.SubSequance). They do not allocate new strings and are more efficient for processing.

To get back a String type, Substring needs to be casted back to String:

let backToString = String(from)

This is where a string is finally allocated.