Considering these observations and more from Brent and Dave, I support
ultimately making KeyPath<T,U>) a subtype of (T)->U as suggested.
If someone really wants this now, I would go with a prefix operator as a
stopgap:
prefix operator ~
prefix 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)
> On Jul 7, 2017, at 11:15 AM, Max Moiseev via swift-evolution
> <[email protected]> wrote:
>
> A few more observations not necessarily supporting either side:
>
> - Why only map, flatMap, and filter? drop, prefix, and sorted can also
> benefit from keyPaths.
> - Adding these overloads only to Sequence will have a very interesting side
> effect on code like: xs.lazy.map(\.name), because lazy. Therefore all these
> overloads will have to be duplicated everywhere.
> - Naive implementation (the one that simply calls the closure taking
> overload) was 4 times slower when I quickly tested it. On the positive side
> though, this same naive implementation does not have to be a part of standard
> library and can easily be provided by a third-party package...
>
> Max
>> On Jul 5, 2017, at 10:08 AM, Benjamin Herzog via swift-evolution
>> <[email protected] <mailto:[email protected]>> wrote:
>>
>> Hey guys,
>>
>> I would like to pitch a small convenient change to the Swift stdlib. With
>> KeyPaths added in SE-0161 I would like to add some convenience calls to map,
>> flatMap and filter in Sequences. To extract properties of an array of
>> objects we currently use trailing closure syntax together with the shorthand
>> $0 for the first closure argument. This is still kind of verbose and also
>> hard to read in some situations.
>> I think it is much better to understand what is going on when using the type
>> safe KeyPaths for that. I already implemented a working solution and would
>> like to pitch the idea here to get some feedback before opening the swift
>> evolution proposal.
>> I propose using
>>
>> persons.flatMap(keyPath: \.name)
>>
>> over
>>
>> persons.flatMap { $0.name }
>>
>> Link to pull request: https://github.com/apple/swift/pull/10760
>> <https://github.com/apple/swift/pull/10760>
>>
>> Link to proposal draft:
>> https://github.com/BenchR267/swift-evolution/blob/keypath-based-map/proposals/0181-keypath-based-map-flatmap-filter.md
>>
>> <https://github.com/BenchR267/swift-evolution/blob/keypath-based-map/proposals/0181-keypath-based-map-flatmap-filter.md>
>>
>> Thanks in advance for your feedback!
>> ______________________
>>
>> Benjamin Herzog
>>
>> _______________________________________________
>> swift-evolution mailing list
>> [email protected] <mailto:[email protected]>
>> https://lists.swift.org/mailman/listinfo/swift-evolution
>
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