Create non-optional in guard to test guarded condition [duplicate]

Question

I currently have a function like this...

// this is a property
var currentString: String = ""

func doSomething() {
    let newString: String = goGetANewString()

    guard newString != currentString else {
        return
    }

    currentString = newString
}

But I find it a bit odd that I am creating the newString outside of the guard.

If I move it into the guard then it complains that it needs to be optional.

Is there a way of creating that newString inside the guard statement and checking the condition?

Ideally I'd like something like this, but like I said, it doesn't work this way.

func doSomething() {
    guard let newString: String = goGetANewString(), newString != currentString else {
        return
    }

    currentString = newString
}

Answer 1

The "trick" is to use guard case with a value-binding pattern for the assignment:

func doSomething() {
    guard case let newString = goGetANewString(), newString != currentString else {
        return
    }

    currentString = newString
}