is duplicated by:

• SR-5371 Allow subclass have throwing initializer when superclass don't

Issue Description:

So, suppose you want to make a subclass of, say, InputStream, and initialize it to a URL, like so:

class InputStream {
    init(url: URL) throws {
        ...
    }
}

An error is returned: "Cannot override non-throwing initializer with throwing initializer." This error seems spurious:

• Initializers aren't inherited, so why does it matter if an initializer has the same signature as one of the superclass's? None of the superclass initializers can even be called outside of a 'super' call in one of our initializers, so for the most part they're living in entirely independent fiefdoms.

• This isn't really even an override; init?(url🙂 translates to initWithURL:, whereas init(url🙂 throws translates to initWithURL:error:. Two entirely different signatures, and a pattern that would have worked without incident in Objective-C.

The unfortunate end result of this situation is that one either has to lose error information in failure conditions, or give the initializer a suboptimal name.