Зачем нужен класс Nothing?

Nothing is a data type that has no values. It is useful when you need to indicate the absence of a return value or that the execution of code never reaches a certain point.

For example:

• In lambda expressions that always throw an exception: The compiler understands that code after such a lambda is unreachable.

  fun fail(message: String): Nothing {
      throw IllegalStateException(message)
  }
  
  val x = fail("Something went wrong") // x has type Nothing
  println("This line will never be executed")
  

• As a return type for functions that never complete normally: For example, an infinite loop.

  fun loopForever(): Nothing {
      while (true) {
          // Infinite loop
      }
  }
  

• For more precise typing in generic functions: Indicates that the type cannot be instantiated.