Exercise: Inline functions
Implement the following inline functions:
anyOfextension onIterable<*>, that returnstrueif any element is of the given type.firstOfOrNullextension onIterable<*>, that returns first element of the given type ornullif there is no such element.filterValuesInstanceOfextension onMap<*, *>that returns a map with only entries that have specified types of both keys and values.
Example usage:
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>()) // {}
This problem can either be solved in the below playground or you can clone kotlin-exercises project and solve it locally. In the project, you can find code template for this exercise in functional/base/Inline.kt. You can find there example usage and unit tests.
Hint: This exercise can be solved using any, firstOrNull, and filter functions, which will be discussed in the next chapter. If you do not know them yet, you can solve this exercise using the for loop, or you can leave it for later.
Once you are done with the exercise, you can check your solution here.
Playground
import org.junit.Test
import kotlin.reflect.typeOf
import kotlin.test.assertEquals
// TODO
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)
}
}
