> On Nov 15, 2017, at 7:36 PM, Greg Parker via swift-evolution
> <[email protected]> wrote:
>
>>
>> On Nov 15, 2017, at 2:31 PM, BJ Homer via swift-evolution
>> <[email protected] <mailto:[email protected]>> wrote:
>>
>>> On Nov 15, 2017, at 3:05 PM, Tino Heth via swift-evolution
>>> <[email protected] <mailto:[email protected]>> wrote:
>>>
>>> Odd… exactly that is the reason why I think filterMap is the worst choice:
>>>
>>> Both are established terms of art, but one has a meaning that doesn’t fit
>>> to the operation.
>>> Applying filter can remove elements, but it can never change types (I feel
>>> kind of silly to repeat this over and over, but so far, nobody took the
>>> time to falsify this).
>>
>> The concern about filter changing types is only relevant if you think of the
>> filter applying to the result of the map, instead of being a part of the
>> filterMap operation itself (an operation that is distinct from map).
>>
>> Let’s imagine that we had this instead:
>>
>> enum SelectiveMapResult<T> {
>> case use(T)
>> case ignore
>> }
>>
>> extension Sequence {
>> func selectiveMap<T>(_ selectiveTransform:
>> (Element)->SelectiveMapResult<T>) -> [T]
>> }
>>
>> let actualNumbers =
>> ["1", "2", "apple", "banana", "5"].selectiveMap({
>> (x)->SelectiveMapResult<Int> in
>> if let value = Int(x) { return .use(value) }
>> else { return .ignore }
>> })
>>
>> actualNumbers == [1, 2, 5]
>>
>> The “selective” part of this operation doesn’t feel like it’s changing the
>> type of the result, because SelectiveMapResult is easily understood to not
>> be part of the mapping transformation; it just exists to tell us whether we
>> should use the result of that particular transformation. Likewise, I don’t
>> feel like the optional in filterMap is part of the mapping operation; it’s
>> just serving the same role as SelectiveMapResult. (It should be obvious that
>> SelectiveMapResult is just Optional with another name here.)
>
> "selectiveMap" feels better in part due to grammar. "map" is obviously the
> verb and "selective" is obviously a modification of "map". "selectiveMap" is
> therefore performing some sort of special map operation.
>
> "filterMap" feels bad for the same reason that "selectMap" would feel worse
> than "selectiveMap". "filter" and "map" are both verbs in this context.
> Grammatically the analogue to "selectiveMap" would be "filteredMap" or
> "filteringMap".
>
> But even then "filteredMap" or "filteringMap" is insufficient to describe the
> operation. You additionally need to know that the "filter" here is not
> ordinary "filter", but instead the special case "filter { $0 != nil }".
>
>
>> The name filterMap focuses on removing the ignored values, as does
>> compactMap. The name selectiveMap focuses on retaining the non-ignored
>> values. I’m not sure whether focusing on the positive or negative aspects is
>> clearer here. I don’t particularly like the name compactMap, simply because
>> I don’t have a lot of experience with languages that use “compact” to mean
>> “drop the nil values”, and without that experience it doesn’t seem
>> intuitive. I think filterMap is better. But if we introduced
>> Sequence.compact() alongside .compactMap(), I’d probably get used to it.
>
> Swift doesn't use "filter" to mean "drop the nil values" either.
>
>
> "compactMap" is okay if "compact" is added. Is "compact" a common enough
> operation in practice to pull its own weight?
>
> "mapSome" is great if you know about Optional.Some but terrible if you don't.
> ("Okay, it maps some elements, but which ones?")
>
> "mapNonNil" is obvious and ugly and perhaps its obviousness makes it a winner.
mapSome and especially mapNonNil both sound to me like they only map the
non-nil values in the source sequence.
John.
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