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

[Adam Sharp]

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