[swift-evolution] Pitch: Support for map and flatMap with smart key paths

[Dave Abrahams]

on Fri Jun 09 2017, Saagar Jha <swift-evolution at swift.org> wrote:

> It reads better and feels more natural. In my mind, it’s similar to the difference between 
>
> ["1", "2", "3"].flatMap { Double($0) }
>
> and
>
> ["1", "2", "3"].flatMap(Double.init)
>
> Saagar Jha

I am not convinced this syntactic sugar is worth complicating the
language or library for, but if it is, IMO the right thing is to make a
keypath be-a subtype of the appropriate function type, rather than to
start down the path of creating a keypath overload for every method that
takes a closure argument.

>
>> On Jun 9, 2017, at 16:06, Max Moiseev via swift-evolution <swift-evolution at swift.org> wrote:
>> 
>> Sorry. I might be missing something. Why is this better than:
>> 
>> let allEmployees = Set(managers.flatMap { $0.directReports }
>> 
>> ?
>> 
>>> On Jun 7, 2017, at 10:35 AM, Adam Sharp via swift-evolution
>>> <swift-evolution at swift.org> wrote:
>>> 
>>> The new smart key path feature is really lovely, and feels like a great addition to Swift.
>>> 
>>> It seems like it might be straightforward to add overloads of `map`
>>> and `flatMap` to the standard library to make use of the new
>>> functionality:
>>> 
>>> 	let managers = flatOrganisation.managers
>>> 	let allEmployees = Set(managers.flatMap(\.directReports))
>>> 	let employeeNames = Set(allEmployees.map(\.name))
>>> 
>>> This feels like a really natural way of working with key paths in a
>>> functional style. It makes a lot of sense for collections, and
>>> possibly for Optional too (although as far as I can see optional
>>> chaining is more or less equivalent, and with more compact syntax).
>>> 
>>> I’m hoping that this might be low-hanging fruit that could be
>>> considered for the Swift 4 release. I’d be happy to have a go at
>>> writing a proposal if there’s interest!
>>> 
>>> –Adam
>>> 
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>> 
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-- 
-Dave