safe.md

``` kotlin fun reply(condition: Boolean): String? = // Nullability is part of Kotlin’s type system if (condition) "I'm fine" else null

fun error(): Nothing = // Always throw an exception throw IllegalStateException("Shouldn't be here")

fun main() { val condition = true // Try replacing true with false and run the sample! val message = reply(condition) // The result is nullable // println(message.uppercase()) // This line doesn't compile println(message?.replace("fine", "okay")) // Access a nullable value in a safe manner if (message != null) { // If you check that the type is right, println(message.uppercase()) // the compiler will smart-cast it for you }

val nonNull: String = // If the null-case throws an error, reply(condition = true) ?: error() // Kotlin can infer that the result is non-null println(nonNull) }

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