In what cases and for what is the Nothing type used in programming?

In Kotlin, the Nothing type is used to denote a function or expression that never returns a value, meaning it does not complete normally. It can be a function that always throws an exception or runs infinitely.

Using the Nothing type is helpful for the compiler to understand that after calling such a function, the code will not continue. For example, a function:

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

Here, fail will never return control to the caller. This aids in code analysis and can, for instance, prevent warnings about uninitialized variables or unreachable code.

Thus, Nothing is used for:

• Denoting functions that do not return a value (e.g., throw exceptions).
• Assisting the compiler in flow analysis.
• Representing the empty type that has no values.