I got a function like this. ``` override fun ...

# arrow

[Hexa]

I got a function like this.

override fun getCar(name: String): Either<CarNotFound, String?> {
        val carAttributes = loadCarAttributes(name)
        return when (carAttributes) {
            is Either.Right -> {
                return Right(carAttributes.b.attributes["carId"])
            }
            is Either.Left -> {
                Left(CarNotFound("car not found"))
            }
        }
    }

When I call that function I want to access the values so that if the value is Left then I just return CarNotFound to the client.
Else I use the value on the Right (which is just a string) to do further processing. I tried something like this but it didnt't work

val carType = getCar("testname").fold( 
                        return Left({CarNotFound(it.message)}),
                        {it})
                )

[Mike]

Both parameters to fold are Lambdas, so that’s one thing.

Also why are you doing a fold when getCar will already return a Left(CarNotFound("car not found")).

[streetsofboston]

I’m not understanding the 2nd snippet, calling the getCar method.

The first param of fold is a return expression, meaning that it returns a value of type Nothing. After the return a Left value holding a lambda is created.
The 2nd parameter of fold returns just the String.

[streetsofboston]

@Hexa What would you like the type of carType to be?

[Hexa]

String

[streetsofboston]

The id of the car. What if it was a left/error value. What should carType be then (type and value)?

[Mike]

and what does loadCarAttributes return? It appears it returns an Either, so perhaps you need to fold it or loadCarAttributes should return an Option, in which case that code could use toEither() on the response.

I think more code/context is required to correctly analyze this, and suggest improvements.

[streetsofboston]

@Hexa something like this?

const val NO_ID = ""

val carType : String = getCar("testname")
    .fold(
        { NO_ID },
        { it }
    )

[Hexa]

yea @Mike loadCarAttributes returns an Either

[Hexa]

thanks @streetsofboston that seems to work

[streetsofboston]

Instead of fold here, you could use getOrDefault or getOrElse or getOrHandle instead (not sure which one works on an Either). Less typing

[Hexa]

I use getOrElse in the end then i just have a separate that if (cartype == NO_ID) return CarNotFound("car not found")

[streetsofboston]

@Hexa
But carType is a String. CarNotFound is not a String.
Your getCar already handles this by returning an Either of CarNotFound and String….. I’m not sure what the code that calls getCar(...) should return then…

[Hexa]

@streetsofboston sorry I meant

if (cartype.equals(NO_ID)) { return CarNotFound("car not found")}

[streetsofboston]

And what does your code return if carType is not equal to NO_ID?