Swift报错：“‘nil‘ is incompatible with return type ‘User‘”

func getUserById(userId: Int) -> User {
    if (userId != nil) {
        ...
    }
    return nil
}

The above code reported an error: "'nil' is incompatible with return type 'User'", indicating that "nil" is incompatible with the return type "User".

solution:

Change the return value type to Optional type User?

func getUserById(userId: Int) -> User? {
    if (userId != nil) {
        ...
    }
    return nil
}

In the same way, if you call getUserById(nil), an error will be reported: "'nil' is not compatible with expected argument type 'Int'"

Just change the parameter type to Int?

func getUserById(userId: Int?) -> User? {
    if (userId != nil) {
        ...
    }
    return nil
}