Enumerationswift 6.0.1Swift

    Never

    A type that has no values and can’t be constructed.

    @frozen enum Never
    Mangled symbol

    ss5NeverOWhat are these?

    FNV24: [G4XX]

    Use Never as the return type of a function that doesn’t return normally — for example, because it runs forever or terminates the program.

    // An infinite loop never returns.
func forever() -> Never {
    while true {
        print("I will print forever.")
    }
}

// Calling fatalError(_:file:line:) unconditionally stops the program.
func crashAndBurn() -> Never {
    fatalError("Something very, very bad happened")
}

    A function that returns Never is called a nonreturning function. Closures, methods, computed properties, and subscripts can also be nonreturning.

    There’s no way to create an instance of Never; this characteristic makes it an uninhabited type. You can use an uninhabited type like Never to represent states in your program that are impossible to reach during execution. Swift’s type system uses this information — for example, to reason about control statements in cases that are known to be unreachable.

    let favoriteNumber: Result<Int, Never> = .success(42)
switch favoriteNumber {
case .success(let value):
    print("My favorite number is", value)
}

    In the code above, favoriteNumber has a failure type of Never, indicating that it always succeeds. The switch statement is therefore exhaustive, even though it doesn’t contain a .failure case, because that case could never be reached.

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