require

inline fun require(value: Boolean)(source)

Throws an IllegalArgumentException if the value is false.

Since Kotlin

1.0

Samples

import kotlin.test.*

fun main() { 
   //sampleStart 
   fun getIndices(count: Int): List<Int> {
    require(count >= 0) { "Count must be non-negative, was $count" }
    // ...
    return List(count) { it + 1 }
}

// getIndices(-1) // will fail with IllegalArgumentException

println(getIndices(3)) // [1, 2, 3] 
   //sampleEnd
}
xxxxxxxxxx
 
fun getIndices(count: Int): List<Int> {
    require(count >= 0) { "Count must be non-negative, was $count" }
    // ...
    return List(count) { it + 1 }
}
// getIndices(-1) // will fail with IllegalArgumentException
println(getIndices(3)) // [1, 2, 3] 
Open in Playground →
Target: JVMRunning on v.2.1.20

inline fun require(value: Boolean, lazyMessage: () -> Any)(source)

Throws an IllegalArgumentException with the result of calling lazyMessage if the value is false.

Since Kotlin

1.0

Samples

import kotlin.test.*

fun main() { 
   //sampleStart 
   fun getIndices(count: Int): List<Int> {
    require(count >= 0) { "Count must be non-negative, was $count" }
    // ...
    return List(count) { it + 1 }
}

// getIndices(-1) // will fail with IllegalArgumentException

println(getIndices(3)) // [1, 2, 3] 
   //sampleEnd
}
xxxxxxxxxx
 
fun getIndices(count: Int): List<Int> {
    require(count >= 0) { "Count must be non-negative, was $count" }
    // ...
    return List(count) { it + 1 }
}
// getIndices(-1) // will fail with IllegalArgumentException
println(getIndices(3)) // [1, 2, 3] 
Open in Playground →
Target: JVMRunning on v.2.1.20

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