[swift-evolution] [Draft] Apply -ed/-ing rule to core functional methods (e.g. filter => filtered)

[Vladimir.S]

On 17.06.2016 8:02, Patrick Pijnappel via swift-evolution wrote:
>     -1, for the same reasons stated on the thread. These are neither
>     guaranteed to be mutating or non-mutating until you get to Collection.
>     Changing map() to mapped() would be lying to the developer some of the
>     time about the mutability of the interface.
>     -DW
>
>
> Actually the -ed/-ing suffix is *not *intended to guarantee
> non-mutatability. It merely communicates whether it is a
> "return-a-transformed-version-of-the-instance"-type method as opposed to an
> in-place mutation. Clearly these are not in-place forms. Note that this is
> my interpretation of the intent of the guidelines (or what should be the
> intent) – if the core team agrees perhaps this deserves clarification in
> the document.

Totally agree with you. I also understand this rule as separation of 
"in-place"/"returns transformed version". I.e. the suffix should say just 
"result of this operation will be returned and should be assigned to other 
instance variable". Otherwise, as I understand, ANY method that will touch 
or iterate the Sequence *could* mutate it and so potentially we should have 
no -ing/-ed methods for Sequence - no?

>
>     These functions are different than for example `sort` because there
>     can’t be a general mutating method of `map`. A variable of type `[A]`
>     can’t be mutated to hold a `[B]` which would be the result of a map
>     from `A -> B`.
>
>
> There could definitely be an in-place variant of filter. While a /fully/
> general method would not be possible for the others, an user might
> reasonable expect in-place variants of map/flatMap if T == U as with e.g. {
> $0 * 2 } or Optionals, and of dropFirst/dropLast if SubSequence == Sequence
> as with e.g. String.
>
> Also note that the -ed/-ing rule should not be merely for ambiguous cases,
> it should tell the user that the main use of the method is returning a
> transformed version of the instance. Having this be a rule you can depend
> on is important.

+1

>
>     -1 The Term of Art argument is very strong with these functions. I
>     prefer them as-is.
>
>
> What specific benefits do we obtain from using the /exact /terms of art vs.
> the very slightly modified versions proposed?

Although I believe we can leave map&reduce as-is, I can understand if we'll 
change them to mapped/reduced and will have consistent naming everywhere, 
don't think this will cause any confusion for one who will start to use 
them. In any case, we can add a hint in compiler like "did you mean 'mapped'?".

>
>
> On Fri, Jun 17, 2016 at 3:24 AM, Brent Royal-Gordon via swift-evolution
> <swift-evolution at swift.org <mailto:swift-evolution at swift.org>> wrote:
>
>     > The 'reduce()' at its core take an array of element and reduce it to single element (could be of a different type) as such it cannot ever be mutating (if one really want it, one could reduce an array to the same array but it is not the goal of the function). For this one it sound to me nearly like asking to rename 'max()' to 'maxed()', 'count' to 'counted' or implement a 'summed()' instead of a 'sum()' for [Int].
>
>     `max`, `count`, and `sum` are all nouns—at least in the senses they are
>     meant in those calls—so they do not take the -ed/-ing suffixes to form
>     immutable variants. Instead, they would take the `form` prefix to form
>     mutable variants, if they had them.
>
>     `map`, `filter`, and `reduce`—at least in the senses they must be
>     interpreted in for the names of those calls to make sense—are verbs,
>     and so they *would* normally take -ed/-ing suffixes. However, as
>     broadly-accepted terms of art, we have left them alone until now.
>
>     --
>     Brent Royal-Gordon
>     Architechies
>
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