ensure

@JvmInline
value class CountryCode(val code: String)

sealed interface CountryCodeError {
    data class InvalidLength(val length: Int) : CountryCodeError
    object ContainsInvalidChars : CountryCodeError
}

fun Raise<CountryCodeError>.countryCode(rawCode: String): CountryCode {
    ensure(rawCode.length == 2) { CountryCodeError.InvalidLength(rawCode.length) }
    ensure(rawCode.any { !it.isLetter() }) { CountryCodeError.ContainsInvalidChars }
    return CountryCode(rawCode)
}

fun main() {
    recover({
        countryCode("US") // valid
        countryCode("ABC") // raises CountryCode.InvalidLength error
        countryCode("A1") // raises CountryCode.ContainsInvalidChar
    }) { error ->
        // Handle errors in a type-safe manner
        when (error) {
            CountryCodeError.ContainsInvalidChars -> {}
            is CountryCodeError.InvalidLength -> {}
        }
    }

    // Can call it w/o error handling => prone to runtime errors
    countryCodeOrThrow("Will fail")
    countryCode("Will fail") // this line won't compile => we're protected

    try {
        countryCodeOrThrow("US") // valid
        countryCodeOrThrow("ABC") // throw IllegalArgumentException
        countryCodeOrThrow("A1") // throw IllegalArgumentException
    } catch (e: IllegalArgumentException) {
        // Not easy to handle
    }
}

// Not type-safe alternative using require
@Throws(IllegalArgumentException::class)
fun countryCodeOrThrow(rawCode: String): CountryCode {
    require(rawCode.length == 2) { CountryCodeError.InvalidLength(rawCode.length) }
    require(rawCode.any { !it.isLetter() }) { CountryCodeError.ContainsInvalidChars }
    return CountryCode(rawCode)
}