[swift-evolution] Optional comparison operators

[Jacob Bandes-Storch]

You'd have to unwrap it, or use the ??/==/!= operators:
https://gist.github.com/jtbandes/9d88cc83ceceb6c62f38

I'd be okay with </<=/>/>= returning Bool?, as I suggested in an older
email (which somehow didn't make it to gmane's archive, but it's quoted in some
other messages
<http://thread.gmane.org/gmane.comp.lang.swift.evolution/10095>). I think
it would be more convenient in some cases than unwrapping the individual
values before comparing them.

Jacob

On Mon, Jul 11, 2016 at 8:08 PM, Saagar Jha <saagarjha28 at gmail.com> wrote:

> Correct me if I’m wrong, but wouldn’t you have to unwrap every comparison
> then?
>
> On Jul 11, 2016, at 20:02, David Sweeris via swift-evolution <
> swift-evolution at swift.org> wrote:
>
> Why not have them return a `Bool?`? If both arguments are non-nil, it can
> return the results of the comparison, otherwise it can return nil.
>
> - Dave Sweeris
>
> On Jul 7, 2016, at 16:37, Jacob Bandes-Storch via swift-evolution <
> swift-evolution at swift.org> 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.
>
> Jacob
>
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