[swift-evolution] [Review] SE-0187: Introduce Sequence.filterMap(_:)

[Tino Heth]

> The “think of optionals as collections” explanation is a good way to help people who are confused by the overload. But an even better way would be to not have a confusing overload in the first place.
With the renaming, confusion might strike less often, but with bigger impact (free translation of a real discussion):
A: Cool, filterMap makes much more sense than flatMap!
Me: Why do you thing so?
A: Well, it does a mapping, and then applies a filter to get rid of nils, and that's super useful!
Me: I see. So you can be sure that when you apply the filterMap method, the result doesn’t contain any nil values?
A: Don’t you understand the concept of a filter? Of course, that’s what I just said, you never have to worry about nil!

[me shows a very simple proof that this is completely wrong]

Even here on the mailing lists, people seem to have a wrong understanding of what flatMap actually does, and this is reinforced with the renaming.
It might have no considerable effect on real-world code, because even with false assumptions, correct results are possible — but I really would prefer to leave the name filterMap free for something like this:

extension Collection {
	func filterMap<T>(transform: (Element) -> T, include: (T) -> Bool) -> [T] {
		return self.map(transform).filter(include)
	}
}

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