Typically you’d use
fatalError()
or
preconditionFailure()
for that.
These do exactly the same: terminating the program, therefore the code after this stamement never gets executed. All of the functions that have this behaviour are annotated with the @noreturn attribute
You can also do something like this:
func getInt() -> Int {
fatalError()
}
The function is supposed to return an Int, but because the program never gets to that point, you don’t have to return anything.