What is the 'bottom' type in Kotlin and what is its role in the type system?

In Kotlin, the "bottom" type is a special type that indicates the absence of a value and is usually represented by Nothing. It is a subtype of all types in Kotlin's type system but has no values.

The role of the "bottom" type (Nothing) is to indicate functions or expressions that never complete normally, such as functions that always throw an exception or run infinitely.

Example:

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

Here, fail returns Nothing, which helps the compiler understand that code after this call will not continue, aiding in code analysis and type checking.

Thus, the "bottom" type serves to denote the absence of a return value and helps the type system be more precise and safe.