<div dir="ltr">Key-Paths do support operators and custom functions. How should this work within the context of this proposal?</div><div class="gmail_extra"><br><div class="gmail_quote">2016-04-12 11:14 GMT+02:00 Brent Royal-Gordon via swift-evolution <span dir="ltr"><<a href="mailto:swift-evolution@swift.org" target="_blank">swift-evolution@swift.org</a>></span>:<br><blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex"><span class="">> I very much like this proposal but what bothers me is this doubling of valueForKeyPath(#keyPath(xxx) in the signature of the function.<br>
><br>
> chris.valueForKeyPath(#keyPath(Person.bestFriend.lastName)) // => Groff<br>
><br>
> chris<br>
> .valueForKeyPath(#keyPath(Person.friends.firstName)) // => ["Joe", "Douglas"]<br>
><br>
> I’m not sure whether the form below is actually possible. For me it reads more naturally and is more consistent with “Modern Swift” as far as I know.<br>
><br>
> chris.valueFor(#keyPath(Person.friends.firstName)) // => ["Joe", "Douglas”]<br>
> or maybe<br>
> chris.valueOf(#keyPath(Person.friends.firstName)) // => ["Joe", "Douglas”]<br>
<br>
</span>Interesting.<br>
<br>
If Foundation, Core Data, AppKit, and other frameworks properly annotated their APIs, I think we could actually get this from the already accepted SE-0033 "Import Objective-C Constants as Swift Types" <<a href="https://github.com/apple/swift-evolution/blob/master/proposals/0033-import-objc-constants.md" rel="noreferrer" target="_blank">https://github.com/apple/swift-evolution/blob/master/proposals/0033-import-objc-constants.md</a>>. Specifically, Foundation would have to include this typedef:<br>
<br>
typedef NSString * NSKeyPath __attribute__((swift_wrapper(struct)));<br>
<br>
And all APIs with string types which were actually key paths would have to be modified to use it. Then `-(nullable id)valueForKeyPath:(NSKeyPath)keyPath` would import as `func value(for: NSKeyPath) -> AnyObject?`. This proposal's `#keyPath` construct would have to then construct an `NSKeyPath` instead of a `String`.<br>
<br>
(To make this all work, it might make sense to add a KeyPathLiteralConvertible protocol to the standard library. As a bonus, if this protocol's initializer received enough metadata, it might be able to construct alternate forms of key paths, such as the Rails-style ones which handle arrays somewhat differently from Foundation's.)<br>
<br>
This is more work, but it's also more general, which is a pretty cool prospect!<br>
<span class="HOEnZb"><font color="#888888"><br>
--<br>
Brent Royal-Gordon<br>
Architechies<br>
<br>
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