I really like the pattern og validated data types....

# arrow

[J]

I really like the pattern og validated data types. In Kotlin I've seen it done like this

@JvmInline
value class Email(val value: String) {
    companion object {
        private const val emailRegex = "^[A-Za-z0-9+_.-]+@[A-Za-z0-9.-]+\$"
        fun from(email: String): Either<FieldValidationFailure, Email> =
            either {
                ensure(email.matches(emailRegex.toRegex())) { InvalidEmail(email) }
                Email(email)
            }
    }
}

However i really dislike having to .value to get the actual values out whenever I need them. Are there any other ways of doing this in kotlin?

[Alejandro Serrano.Mena]

not really if you want to keep the type safety

[David]

Also an addition, do prevent unwanted creations of Email it could be worth make it's constructor private:

value class Email private constructor(val value: String) {

[dave08]

You could inherit the Email class from CharSequence by value

[J]

Could you elaborate on that Dave?

[dave08]

@JvmInline
value class Email(val value: String): CharSequence by value {
    companion object {
        private const val emailRegex = "^[A-Za-z0-9+_.-]+@[A-Za-z0-9.-]+\$"
        fun from(email: String): Either<FieldValidationFailure, Email> =
            either {
                ensure(email.matches(emailRegex.toRegex())) { InvalidEmail(email) }
                Email(email)
            }
    }
}

[dave08]

Then all the CharSequence functions are delegated to Email @J. But you'd maybe loose the gains of a value class (?)...