I like this promote operator idea. I have been defining similar operators for
specific projects almost at random. It makes sense to come up with a
well-defined behavior and name for such operators, as a common practice as you
suggest.
The problem with the postfix operator is that it does not currently work
without an extra set of parenthesis:
postfix operator ^
postfix func ^<T,U>(lhs: KeyPath<T,U>) -> (T)->U { return { $0[keyPath: lhs] } }
struct Guy { let name: String }
let guys = [
Guy(name: "Benjamin"),
Guy(name: "Dave"),
Guy(name: "Brent"),
Guy(name: "Max")
]
guys.map(\.name^) // Error: Invalid component of Swift key path
guys.map((\.name)^) // This works
Is this a bug?
That is the reason I used a prefix operator (~) in my suggestion in the a
previous e-mail on this thread.
> On Jul 7, 2017, at 4:27 PM, Dave Abrahams via swift-evolution
> <[email protected]> wrote:
>
> By the way, if you're worried about whether subtyping will fly, I've
> recently been thinking there might be a role for a “promotion” operator
> that enables lossless “almost-implicit” conversions, e.g.:
>
> someNumber^ is equivalent to numericCast(someNumber)
> \.someKeyPath^ is equivalent to { $0\.someKeyPath }
> someSubstring^ is equivalent to String(someSubstring)
>
> etc.
>
> This convenience can be implemented by anyone today for keypaths, and
> will provide nearly the syntax you're looking for. This is exactly the
> sort of thing I'd love to see become a widespread existing practice
> before we incorporate it in the standard library, so we could properly
> judge its impact on real code.
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