[swift-evolution] Optional comparison operators

[Mark Lacey]

> 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 <mailto: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 <mailto: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 <mailto: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.devel/2089>
>> - http://thread.gmane.org/gmane.comp.lang.swift.evolution/10095 <http://thread.gmane.org/gmane.comp.lang.swift.evolution/10095>
>> - rdar:// <>16966712&22833869
>> - Replies to https://twitter.com/jtbandes/status/646914031433871364 <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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