requireNotNull

Platform and version requirements: JVM (1.0), JS (1.0), Native (1.0)

fun <T : Any> requireNotNull(value: T?): T

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

Platform and version requirements: JVM (1.0), JS (1.0), 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.uppercase())
}

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
}

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Licensed under the Apache License, Version 2.0.
https://kotlinlang.org/api/latest/jvm/stdlib/kotlin/require-not-null.html