As far as the Sequence overloads: I really, really think we should go a step
beyond renaming and separate the functions into the underlying operations.
FlatMap has three separate and orthogonal effects, so it should be split into
three functions—flatten, map, and dropNil. Map already exists, obviously, but
flatten and dropNil (or compact[ed], as I've seen suggested) are independently
useful—I've used `.flatMap { $0 }` several times, and I've written my own
`flatten` because I didn't actually realize there was a separate overload for
that (I don't want to sound rude to the Apple devs who decided on that, but…
why on earth was an already confusing name overloaded with unrelated
functionality instead of using the term of art?).
For Optional, I suggest mapValue.
> On Nov 16, 2017, at 8:11 AM, Erica Sadun via swift-evolution
> <swift-evolution@swift.org> wrote:
>
>
> I like `mapSome`:
>
> * `mapSome` uses conventional Swift terminology.
> * It makes the outcome and expectations clear.
> * As a bonus, it combines the English meaning of "some" ("map across some of
> these items", as in creating a filtered result) and the `Optional` case name.
>
> In response to John's "mapSome and especially mapNonNil both sound to me like
> they only map the non-nil values in the source sequence.", I'd respond that
> the mode of action is:
>
> 1. apply the function
> 2. retrieve `some` cases
>
> Selecting `mapSome` reflects those two stages. There is, however, Kevin's
> (sound) point against that it "sounds like it takes a sequence of optionals
> and only modifies the non-nil values", but I still like it. Some of the
> suggestions built around unwrapping address John's concern, for example
> `mapUnwrapped` but fail to distinguish between the `some` and `nil` cases,
> suggesting perhaps a catastrophic outcome for nil values.
>
> I could live with many of the other names but I dislike `compact` (it has no
> precedent, sets an expectation of the implementation which may not match
> reality). Similarly `mapReduce` or `mapReducing` (which I prefer to
> `reduceMap`) may overburden the expectation of the existing `reduce`, where a
> user thinks prior results feed into the output, which they don't. I
> moderately like `mapSelective` (over `selectiveMap`) but I like it less than
> `filterMap`, `mapFiltering`, or `mapFiltered` and `mapSome`, all of which use
> Swift terms of art in their naming. (Also note Gwendal's finding that as a
> term of art, it has "a different signature, and a different meaning" in
> RxSwift.)
>
> Summary:
>
> * I like `mapSome`
> * I'm fine with a `filter` variation, of which I prefer `mapFiltered`
>
> -- E, former supporter of `filterMap` before `mapSome` entered her awareness
>
>
>> On Nov 15, 2017, at 2:15 PM, Ben Cohen via swift-evolution
>> <swift-evolution@swift.org <mailto:swift-evolution@swift.org>> wrote:
>>
>> I continue to favour mapSome, since it’s both literally and figuratively
>> what it does, but appreciate that exposing the name of the Optional.some
>> case isn’t to everyone’s taste.
>>
>>> On Nov 15, 2017, at 12:55 PM, John McCall via swift-evolution
>>> <swift-evolution@swift.org <mailto:swift-evolution@swift.org>> wrote:
>>>
>>> Hello, Swift Community!
>>>
>>> The initial review of "SE-0187: Introduce Sequence.filterMap(_:)" ran
>>> through yesterday, November 14th, 2017. The proposal is available here:
>>>
>>> https://github.com/apple/swift-evolution/blob/master/proposals/0187-introduce-filtermap.md
>>>
>>> <https://github.com/apple/swift-evolution/blob/master/proposals/0187-introduce-filtermap.md>
>>>
>>> There was a significant amount of discussion, and people came down with
>>> reasonable arguments both for and against the proposal. After reviewing
>>> that feedback, the core team feels that the central question is whether
>>> Swift benefits from overloading flatMap in this way. There is a reasonable
>>> argument that an Optional is a sort of container, and therefore it makes
>>> sense to "flatten" that container into a surrounding container. But Swift
>>> has resisted applying that interpretation in its library design; for
>>> example, you cannot directly iterate an Optional or append its contents to
>>> an Array. In general, we feel that using different operations for working
>>> with Optionals tends to make code easier to both write and understand,
>>> especially given the existence of implicit optional promotion, which we
>>> cannot eliminate or easily suppress based on the context. On reflection,
>>> we think it was a mistake to use the same name in the first place, and
>>> there is no better time to fix a mistake than now.
>>>
>>> While we accept that this will cause some amount of "code churn" for
>>> developers when they adopt Swift 5, the required change is a simple rename
>>> that should be painless to automatically migrate. Of course, sample code
>>> on the internet will become obsolete, but fix-its will easily update that
>>> code if pasted into a project, and the samples themselves (once corrected)
>>> should become clearer and easier to teach after this change, as is
>>> generally true when overloading is removed.
>>>
>>> Accordingly, SE-0187 is accepted, at least as far as not calling the
>>> operation "flatMap". We are re-opening the review until next Monday,
>>> November 20th, 2017, in order to have a focused discussion about the new
>>> name. Names that seemed to gain some traction in the first review include:
>>>
>>> - filterMap, which has precedent in existing functional languages, as
>>> well as some popular Swift libraries, but which some people view as
>>> confusing
>>>
>>> - compactMap, which builds off the precedent of "compact" in Ruby
>>>
>>> But please feel free to suggest a name other than these.
>>>
>>> Reviews
>>>
>>> Reviews are an important part of the Swift evolution process. All reviews
>>> should be sent to the swift-evolution mailing list at
>>>
>>> https://lists.swift.org/mailman/listinfo/swift-evolution
>>> <https://lists.swift.org/mailman/listinfo/swift-evolution>
>>> or, if you would like to keep your feedback private, directly to me as the
>>> review manager. When replying, please try to keep the proposal link at the
>>> top of the message:
>>>
>>> Proposal link:
>>>
>>> https://github.com/apple/swift-evolution/blob/master/proposals/0187-introduce-filtermap.md
>>>
>>> <https://github.com/apple/swift-evolution/blob/master/proposals/0187-introduce-filtermap.md>
>>> Reply text
>>> Other replies
>>> What goes into a review?
>>>
>>> The goal of the review process is to improve the proposal under review
>>> through constructive criticism and, eventually, determine the direction of
>>> Swift.
>>>
>>> When writing your review, here are some questions you might want to answer
>>> in your review:
>>>
>>> • What is your evaluation of the proposal?
>>> • Is the problem being addressed significant enough to warrant a change
>>> to Swift?
>>> • Does this proposal fit well with the feel and direction of Swift?
>>> • If you have used other languages or libraries with a similar feature,
>>> how do you feel that this proposal compares to those?
>>> • How much effort did you put into your review? A glance, a quick
>>> reading, or an in-depth study?
>>>
>>> More information about the Swift evolution process is available at:
>>>
>>> https://github.com/apple/swift-evolution/blob/master/process.md
>>> <https://github.com/apple/swift-evolution/blob/master/process.md>
>>>
>>> As always, thank you for contributing to the evolution of Swift.
>>>
>>> John McCall
>>> Review Manager
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>>
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