[swift-evolution] Optional comparison operators
davesweeris at mac.com
Mon Jul 11 22:02:02 CDT 2016
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.
> swift-evolution mailing list
> swift-evolution at swift.org
-------------- next part --------------
An HTML attachment was scrubbed...
More information about the swift-evolution