requireNotNull

Common
JVM
JS
Native
1.0
fun <T : Any> requireNotNull(value: T?): T

Throws an IllegalArgumentException if the value is null. Otherwise returns the not null value.

Common
JVM
JS
Native
1.0
inline fun <T : Any> requireNotNull(
    value: T?,
    lazyMessage: () -> Any
): T

Throws an IllegalArgumentException with the result of calling lazyMessage if the value is null. Otherwise returns the not null value.

import kotlin.test.*

fun main(args: Array<String>) {
//sampleStart
fun printRequiredParam(params: Map<String, String?>) {
    val required: String = requireNotNull(params["required"]) { "Required value must be non-null" } // returns a non-null value
    println(required)
    // ...
}

fun printRequiredParamByUpperCase(params: Map<String, String?>) {
    val requiredParam: String? = params["required"]
    requireNotNull(requiredParam) { "Required value must be non-null" }
    // now requiredParam is smartcast to String so that it is unnecessary to use the safe call(?.)
    println(requiredParam.toUpperCase())
}

val params: MutableMap<String, String?> = mutableMapOf("required" to null)
// printRequiredParam(params) // will fail with IllegalArgumentException
// printRequiredParamByUpperCase(params) // will fail with IllegalArgumentException

params["required"] = "non-empty-param"
printRequiredParam(params) // prints "non-empty-param"
printRequiredParamByUpperCase(params) // prints "NON-EMPTY-PARAM"
//sampleEnd
}