[swift-evolution] Optional comparison operators

[Jacob Bandes-Storch]

Personally I think we should just remove these optional-taking variants of
the comparison operators. Does anyone agree/disagree?

It does make sense to keep ==(T?, T?) and !=(T?, T?), and if coercion were
removed, we might want to add (T, T?) and (T?, T) versions. Are there any
other operators that would be affected by your proposal? If not, removing
the optional </<=/>/>= would obviate the need to remove coercion.

Jacob

On Mon, Jul 11, 2016 at 4:45 PM, Mark Lacey <mark.lacey at apple.com> wrote:

>
> On Jul 11, 2016, at 4:32 PM, Jacob Bandes-Storch <jtbandes at gmail.com>
> wrote:
>
> Great, thanks Mark! I look forward to it.
>
>
> To be clear, I’m specifically looking at making the change to remove the
> coercion from T to T? for operator arguments.
>
> I agree there might be other things worth looking at regarding operators
> that take optionals, but I’m not currently looking at those issues.
>
> Mark
>
>
> On Mon, Jul 11, 2016 at 4:31 PM, Mark Lacey <mark.lacey at apple.com> wrote:
>
>> Hi Jacob,
>>
>> On Jul 11, 2016, at 4:23 PM, Jacob Bandes-Storch via swift-evolution <
>> swift-evolution at swift.org> wrote:
>>
>> Bump for Swift 3.
>>
>> On Thu, Jul 7, 2016 at 2:37 PM, Jacob Bandes-Storch <jtbandes at gmail.com>
>> wrote:
>>
>>> These operators cause some potential for confusion:
>>>
>>>     public func <<T : Comparable>(lhs: T?, rhs: T?) -> Bool
>>>     public func ><T : Comparable>(lhs: T?, rhs: T?) -> Bool
>>>     public func <=<T : Comparable>(lhs: T?, rhs: T?) -> Bool
>>>     public func >=<T : Comparable>(lhs: T?, rhs: T?) -> Bool
>>>
>>> 1. The meaning of T? < T? is not immediately obvious (Why is nil <
>>> .some(x) for any x? Personally, my intuition says that Optional should only
>>> provide a partial order, with .none not being ordered w.r.t. .some(x).)
>>>
>>> 2. Even if the meaning is understood, it can be surprising when the (T?,
>>> T?) -> Bool version is used instead of (T, T) -> Bool.
>>>
>>> Prior discussion:
>>> - http://thread.gmane.org/gmane.comp.lang.swift.devel/2089
>>> - http://thread.gmane.org/gmane.comp.lang.swift.evolution/10095
>>> - rdar://16966712&22833869
>>> - Replies to https://twitter.com/jtbandes/status/646914031433871364
>>>
>>> In the swift-dev thread from May, Chris said:
>>>
>>> One of the ideas that Joe Pamer has been discussing is whether the
>>>>> implicit promotion from T to T? should be disabled when in an operator
>>>>> context.  Doing so would fix problems like this, but making the code
>>>>> invalid.
>>>>
>>>>
>>>>
>>> A change like this would be source-breaking, so if the core team has
>>> recommendations for how to handle these issues, now is probably the time to
>>> get it done.
>>>
>>
>> I overlooked your previous message on this.
>>
>> I’m actually writing up a proposal for this now, and have an
>> implementation that I’ve done a bit of testing with.
>>
>> I’m hoping to get the proposal out in the next couple days.
>>
>> Mark
>>
>>
>
>
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