On Wed, Nov 8, 2017, at 02:29 PM, Max Moiseev via swift-evolution wrote:> > >> On Nov 8, 2017, at 12:20 PM, Tino Heth <2...@gmx.de> wrote: >> >> >>> This is a wonderful example! But it’s an argument for a different >>> discussion (of general usefulness of implicit optional promotion). >>> Thanks to the optional promotion, what the closure returns is not >>> nil, but instead is .some(nil), and that is not filtered out.>> My point >>> is: The proposed filterMap isn’t a combination of map and >> filter at all — or can you build it just out of map & filter, like >> flatMap is constructed from map & flatten?> >> https://github.com/apple/swift/blob/master/stdlib/public/core/FlatMap.swift#L49> >> > It *is* a combination of map and filter. It is purely for performance > we don’t do the same thing on any Sequence, because that will allocate > a temporary array or two. Well, that certainly explains the nasty return type. I rather wish we had a LazyFlatMapSequence type rather than using map(…).filter(…).map(…) if for no other reason than it would produce a return type that's easier to work with. -Kevin Ballard
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