[swift-evolution] Optional comparison operators
saagarjha28 at gmail.com
Mon Jul 11 22:08:35 CDT 2016
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 <mailto: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.devel/2089>
>> - http://thread.gmane.org/gmane.comp.lang.swift.evolution/10095 <http://thread.gmane.org/gmane.comp.lang.swift.evolution/10095>
>> - rdar:// <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.
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