factory-function-approach-4.kt

class PhoneNumberScreen private constructor(
    private val phoneNumber: PhoneNumber
) {
    fun render() {
        println("Phone number: ${phoneNumber.value}")
    }

    companion object {
        fun create(phoneNumber: PhoneNumber): PhoneNumberScreen? {
            return when {
                phoneNumber.value.isNotEmpty() -> PhoneNumberScreen(phoneNumber)
                else -> null
            }
        }
    }
}

fun main() {
    val contact = Contact(PhoneNumber("12345"))
    show(contact.phoneNumber) // "Phone number: 12345"

    val contactWithInvalidPhoneNumber = Contact(PhoneNumber(""))
    show(contactWithInvalidPhoneNumber.phoneNumber) // prints nothing
}

private fun show(phoneNumber: PhoneNumber) {
    val phoneNumberScreen = PhoneNumberScreen.create(phoneNumber)
    phoneNumberScreen?.render()
}