Kotlin - no_image

Any, Nothing, Unit

Any the root of the Kotlin class hierarchy. Any is the super type of all non-nullable types. Any can’t hold the null value, for holding null value you can use Any?. Kotlin compiler treats kotlin.Any and java.lang.Object as two different types, but at runtime they are represented with the same java.lang.Object class.

Nothing has no instances. You can use Nothing to represent “a value that never exists”: for example, if a function has the return type of Nothing, it means that it never returns (always throws an exception). Nothing implicity extend any object that exists.

fun fail(message: String): Nothing {
    throw IllegalStateException(message)
}

val address = employee.address ?: fail("${employee.name} has no address defined")
println(address)

// > java.lang.IllegalStateException: John has no address defined

Unit In Java if we want that a function does return nothing we use void, Unit is the equivalent in Kotlin.The main characteristics of Unit against Java’s void are:

• Unit is a type and therefore can be used as a type argument.
• Only one value of this type exists.
• It is returned implicitly. No need of a return statement.

Links

https://itnext.io/kotlin-basics-types-any-unit-and-nothing-674cc858035
https://proandroiddev.com/kotlins-nothing-type-946de7d464fb
https://blog.kotlin-academy.com/kotlins-nothing-its-usefulness-in-generics-5076a6a457f7
https://stackoverflow.com/questions/38761021/does-any-object
https://kotlinlang.org/api/latest/jvm/stdlib/kotlin/-any/
https://kotlinlang.org/api/latest/jvm/stdlib/kotlin/-nothing.html
https://kotlinlang.org/api/latest/jvm/stdlib/kotlin/-unit/

credit goes to @swayangjit