[swift-evolution] Optional comparison operators
jtbandes at gmail.com
Mon Jul 11 18:23:13 CDT 2016
Bump for Swift 3.
On Thu, Jul 7, 2016 at 2:37 PM, Jacob Bandes-Storch <jtbandes at gmail.com>
> 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
> 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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