[swift-evolution] mandatory "?" suffix for identifiers associated with optional types

[Adrian Kashivskyy]

I agree it may lead to unexpected bugs, but "let f = x? < 5" is not a great alternative, either. We should consider rethinking the behavior of comparison function itself, rather than introduce a new language feature like an operator.

I suggest changing the comparison function's return value to an optional Bool? and consider the following implementation

> func < <T: Comparable>(lhs: T?, rhs: T?) -> Bool? {
> 	if let lhs = lhs, rhs = rhs {
> 		return lhs < rhs
> 	} else {
> 		return nil
> 	}
> }


That way,

> // true
> Optional(1) < Optional(2)
> 
> // nil
> Optional(1) < nil
> 
> // nil
> nil < Optional(2)


Pozdrawiam – Regards,
Adrian Kashivskyy

> Wiadomość napisana przez Amir Michail <a.michail at me.com> w dniu 04.12.2015, o godz. 18:30:
> 
>> 
>> On Dec 4, 2015, at 12:27 PM, Adrian Kashivskyy <adrian.kashivskyy at me.com <mailto:adrian.kashivskyy at me.com>> wrote:
>> 
>> I agree with Alex, 
>> 
>>> Optionality is associated with the type, not the identifier.
>> 
>> Optionals are designed to provide null safety inside a program, not promote using nullables wherever possible. If you use optionals so extensively that you feel the need for special IDE support, maybe you should consider rethinking your API.
>> 
>> By the way,
>> 
>>> So for example the following (probable) bug would result in a compile error:
>>> let f = x < 5 // where x is optional and could be nil
>> 
>> I believe nil being less than anything else is an expected behavior which has been introduced by design.
>> 
> 
> It still leads to bugs that are hard to find though.
> 
> In any case, I proposed using this code for such a comparison: let f = x? < 5
> 
>> Pozdrawiam – Regards,
>> Adrian Kashivskyy
>> 
>>> Wiadomość napisana przez Amir Michail <a.michail at me.com <mailto:a.michail at me.com>> w dniu 04.12.2015, o godz. 17:17:
>>> 
>>>> 
>>>> On Dec 4, 2015, at 10:57 AM, Alex Blewitt <alex.blewitt at gmail.com <mailto:alex.blewitt at gmail.com>> wrote:
>>>> 
>>>> 
>>>>> On 4 Dec 2015, at 16:44, Amir Michail <a.michail at me.com <mailto:a.michail at me.com>> wrote:
>>>>> 
>>>>> I don’t want to remember if a variable is optional. I want to see it in the variable name.
>>>> 
>>>> Optionality is associated with the type, not the identifier. In addition, how would you deal with type aliases to optional constructs?
>>>> 
>>>> typealias MaybeString = String?
>>>> var maybe:MaybeString
>>>> 
>>>> This doesn’t ‘look’ like an optional value (so would it deserve a ? at the end) but if you have MaybeString? you now have an Optional<Optional<String>>. Should you have ?? there now?
>>>> 
>>>> Alex
>>> 
>>> You would have:
>>> 
>>> typealias MaybeString? = String?
>>> var maybe?:MaybeString?
>>> 
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