RxSwift convert Observable<String> into String

Question

I've having a problem in RxSwift in converting a Observable into a String.

I understand that an observable is a sequence, I just want the last change in the username.

I'm storing username and password as:

let username = BehaviorRelay<String>(value: "")
let password = BehaviorRelay<String>(value: "")

And previously have used combineLatest

func loginButtonValid(username: Observable<String>, password: Observable<String>) -> Observable<Bool> {
    return Observable.combineLatest(username, password)
    { (username, password) in
        return username.count > 0
            && password.count > 0
            && self.validateEmail(enteredEmail: username)
    }
}

But how can I just take the latest from the username?

I've tried takelast and use combineLatest with just one argument, but neither seems to work.

I want to do this to validate whether an email is valid, and the validate email function I'm using is the following (for reference only):

func validateEmail(enteredEmail:String) -> Bool {
    let emailFormat = "[A-Z0-9a-z._%+-]+@[A-Za-z0-9.-]+\\.[A-Za-z]{2,64}"
    let emailPredicate = NSPredicate(format:"SELF MATCHES %@", emailFormat)
    return emailPredicate.evaluate(with: enteredEmail)
}

My attempts are around the following ideas

func emailValid(username: Observable<String>) -> Observable<Bool> {
        return username.takeLast()
        { (lastusername) in
            return self.validateEmail(enteredEmail: (lastusername) )
        }
}

Answer 1

If I understood correctly, you want to transform an Observable<String> to an Observable<Bool>, which is the job of the map method:

func emailValid(username: Observable<String>) -> Observable<Bool> {
    return username.map(self.validateEmail)
}