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

[BJ Homer]

> On Nov 11, 2017, at 9:49 AM, Michel Fortin via swift-evolution <swift-evolution at swift.org> wrote:
> 
> I think it fits well for arrays. Not sure about optionals.

This proposal only suggests changing the one on sequences, and even then, not all of them. Currently, the following exist:

// Reminder: Int("someString") returns 'Int?' in the following examples

// (1) Sequence.flatMap() with a closure returning an optional, dropping anything that maps to nil
["1", "mountain", "2"].flatMap({ Int($0) })  // [1, 2]

// (2) Sequence.flatMap() with a closure returning a sequence, then joining (“flattening”) them into one array
[1, 2, 3].flatMap({ Array(1...$0) }) // [1, 1, 2, 1, 2, 3]

// (3) Optional.flatMap() with a closure returning an optional, flattening a nested optional.
("3" as String?).flatMap({ Int($0) }) // Optional(3)


The 2nd and 3rd variants are both about flattening nested structures, and would not change under this proposal. We would keep calling them “flatMap()”. There is no a proposal to add Optional.filterMap, nor to change the Sequence.flatMap variant that flattens nested sequences. The only change proposed it is to rename the first one.

-BJ
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