Solution: Inline functions
Solutions using for-loops:
inline fun <reified T> Iterable<*>.anyOf(): Boolean {
for (element in this) {
if (element is T) return true
}
return false
}
inline fun <reified T> Iterable<*>.firstOfOrNull(): T? {
for (element in this) {
if (element is T) return element
}
return null
}
inline fun <reified T, reified R> Map<*, *>
.filterValuesInstanceOf(): Map<T, R> {
val result = mutableMapOf<T, R>()
for ((key, value) in this) {
if (key is T && value is R) {
result[key] = value
}
}
return result
}
Solutions using collection processing functions:
inline fun <reified T> Iterable<*>.anyOf(): Boolean =
any { it is T }
inline fun <reified T> Iterable<*>.firstOfOrNull(): T? =
firstOrNull { it is T } as? T
inline fun <reified T, reified R> Map<*, *>
.filterValuesInstanceOf(): Map<T, R> =
filter { it.key is T && it.value is T } as Map<T, R>
Example solution in playground
import org.junit.Test
import kotlin.reflect.typeOf
import kotlin.test.assertEquals
inline fun <reified T> Iterable<*>.anyOf(): Boolean {
for (element in this) {
if (element is T) return true
}
return false
}
inline fun <reified T> Iterable<*>.firstOfOrNull(): T? {
for (element in this) {
if (element is T) return element
}
return null
}
inline fun <reified T, reified R> Map<*, *>
.filterValuesInstanceOf(): Map<T, R> {
val result = mutableMapOf<T, R>()
for ((key, value) in this) {
if (key is T && value is R) {
result[key] = value
}
}
return result
}
fun main() {
val list = listOf(1, "A", 3, "B")
println(list.anyOf<Int>()) // true
println(list.anyOf<String>()) // true
println(list.anyOf<Double>()) // true
println(list.firstOfOrNull<String>()) // A
println(list.firstOfOrNull<Int>()) // 1
println(list.firstOfOrNull<Double>()) // null
val map = mapOf(1 to 2, 2 to "A", 3 to 4, "B" to "C")
println(map.filterValuesInstanceOf<Int, String>()) // {2=A}
println(map.filterValuesInstanceOf<String, String>()) // {B=C}
println(map.filterValuesInstanceOf<Int, Int>()) // {1=2, 3=4}
println(map.filterValuesInstanceOf<String, Int>()) // {}
}
class InlineTest {
@Test
fun anyOfTest() {
assert(listOf(1, 2, 3, "4").anyOf<Int>())
assert(listOf(1, 2, 3, "4").anyOf<String>())
assert(!listOf(1, 2, 3, "4").anyOf<Double>())
assert(listOf(1, 2, 3).anyOf<Int>())
assert(!listOf(1, 2, 3).anyOf<String>())
val o = object {
val result = listOf(1, 2, 3, "4").anyOf<Int>()
}
assertEquals(typeOf<Boolean>(), o::result.returnType)
}
@Test
fun firstOfOrNullTest() {
assertEquals(1, listOf(1, 2, 3, "4").firstOfOrNull<Int>())
assertEquals("4", listOf(1, 2, 3, "4").firstOfOrNull<String>())
assertEquals(null, listOf(1, 2, 3, "4").firstOfOrNull<Double>())
assertEquals(1, listOf(1, 2, 3).firstOfOrNull<Int>())
assertEquals(null, listOf(1, 2, 3).firstOfOrNull<String>())
val o = object {
val result = listOf(1, 2, 3, "4").firstOfOrNull<Int>()
}
assertEquals(typeOf<Int?>(), o::result.returnType)
}
@Test
fun filterValuesInstanceOfTest() {
assertEquals(
mapOf(1 to 1, 2 to 2, 3 to 3),
mapOf(1 to 1, 2 to 2, 3 to 3, 4 to "4").filterValuesInstanceOf<Int, Int>()
)
assertEquals(
mapOf(4 to "4"),
mapOf(1 to 1, 2 to 2, 3 to 3, 4 to "4").filterValuesInstanceOf<Int, String>()
)
assertEquals(
mapOf(),
mapOf(1 to 1, 2 to 2, 3 to 3, 4 to "4").filterValuesInstanceOf<String, String>()
)
assertEquals(
mapOf(1 to 1, 2 to 2, 3 to 3),
mapOf(1 to 1, 2 to 2, 3 to 3).filterValuesInstanceOf<Int, Int>()
)
assertEquals(
mapOf(),
mapOf(1 to 1, 2 to 2, 3 to 3).filterValuesInstanceOf<Int, String>()
)
val o = object {
val result = mapOf(1 to 1, 2 to 2, 3 to 3, 4 to "4").filterValuesInstanceOf<Int, Int>()
}
assertEquals(typeOf<Map<Int, Int>>(), o::result.returnType)
}
}
