[swift-evolution] When to use argument labels (a new approach)

Radosław Pietruszewski radexpl at gmail.com
Thu Feb 4 02:23:10 CST 2016



> On 04 Feb 2016, at 02:20, Dave Abrahams via swift-evolution <swift-evolution at swift.org> wrote:
> 
> 
> on Wed Feb 03 2016, Radosław Pietruszewski <swift-evolution at swift.org> wrote:
> 
>> Overall, great guidelines (and +1 to the rules Erica wrote up), and
>> I’m +1 on conveying these nuances in the guidelines.
>> 
>>> 2. Words that describe attributes of an *already-existing* instance
>>>  should go in the base name rather than in a label:
>>> 
>>>     a.tracksHavingMediaType("Wax Cylinder")      // yes
>>>     a.removeFirstTrackHavingMediaType("BetaMax") // yes
>>> 
>>>     a.tracks(mediaType: "Wax Cylinder")          // no
>>>     a.removeFirstTrack(havingMediaType: "BetaMax") // no
>>> 
>>>  [yes, we could use "With" instead of "Having", but it's more
>>>  ambiguous]
>>> 
>>>  Words that describe attributes of an instance *to be created* should
>>>  go in argument labels, rather than the base name (for parity with
>>>  initializers):
>>> 
>>>     AudioTrack(mediaType: "BetaMax")                   // initializer
>>>     trackFactory.newTrack(mediaType: "Wax Cylinder")   // yes
>>> 
>>>     trackFactory.newTrackWithMediaType("Wax Cylinder") // no
>> 
>> The rationale for doing this is stronger when we talk about automatic
>> translation of Objective-C APIs.
> 
> For better or worse, it is a requirement that Cocoa as imported very
> closely approximates full conformance to the guidelines we choose.  We
> are shooting for consistency across APIs used in swift.

Hmm. Understood, but sigh. Personally I think it’s a shame to constrain ourselves to (imho) inferior naming convention because it’s what existing ObjC APIs use. Definitely understandable, but considering this isn’t a _really_ super common pattern, I think it would be just fine to leave the translations in good-enough state (whatever the decision on SE-0005 is), and follow a new convention in new Swift APIs.

> 
>> But in APIs designed for Swift, I feel like this is wrong IMHO, because:
>> 
>> - “media type” is still a parameter, so it shouldn’t be in the base
>>  name itself
> 
> That doesn't seem obvious to me.  Whether that "should" be in the base
> name depends on what guidelines we choose.  

Of course. The way I think of it: the primary semantic is “find a track”, and media type is a criterion for search. I understand method families aren’t something you’re looking to optimize, but you can imagine that _if_ this was a family, it would still be “find a track”, just with different criteria.

>> - this breaks the symmetry with other methods due to the reason above
>>  (like the “newTrack” you mentioned yourself) 
> 
> Yes, it would be more consistent if these two cases were the same.  
> 
>> - doesn’t play well with method families (searching for tracks is
>>  searching for tracks. the criteria for search are just parameters).
> 
> I don't really believe that “method families” are something we want to
> optimize for in Swift.  There are almost always alternatives that impose
> lower cognitive overhead on users.

Fair.

> 
>> If we do
>> 
>>   trackFactory.newTrack(mediaType: "Wax Cylinder")   // yes
>> 
>> I don’t see why it’s OK to do
>> 
>>   a.tracksHavingMediaType("Wax Cylinder")      // yes
> 
> That's just the consistency argument again, right?

Yes.

> 
>> Of course just “tracks” is confusing, and we agree on that, but I
>> would strongly recommend that for new APIs we don’t just name the
>> method with a word of an already-existing instance, rather, we start
>> it with a verb:
>> 
>> a.findTracks(mediaType: “BetaMax”) // or “searchTracks”, or alternatively “tracksMatching"
>> a.removeFirstTrackMatching(mediaType: “BetaMax”)   — ad 2
>> fac.newTrack(mediaType: “Wax Cylinder”)
>> 
>> Symmetric, predictable, follows the same convention, plays well with
>> method families (i.e. different search criterion than media type), and
>> no clarity problems.
> 
> Unfortunately, this is the reality:
> 
> 1. The pattern of omitting prefix verbs like “get” and “find” is
>   something of a sacred cow; I think it would be very hard to sell to
>   certain important people.

Hmm, I didn’t think of that. “get” is sort of understandable, I can see how in some languages you’d do “getFoo()”, whereas in Swift it would probably be a property “foo”. I don’t see a problem with “find”, though, as it really does help convey the intent.

> 
> 2. if we were to standardize on the opposite, we would need an
>   objective-C import strategy that would add these verbs automatically.
> 
> If you can get a handle on solving #2, it *might* be worth me taking a
> shot at solving #1. Otherwise, I'm afraid this idea is dead in the
> water.  Nothing that leaves glaring inconsistencies between imported
> Cocoa and the API guidelines is going to be acceptable.

Then perhaps let’s meet halfway:

   a.tracksWith(mediaType: “BetaMax”)
   a.removeFirstTrackWith(mediaType: “BetaMax”)
   fac.newTrack(mediaType: “Wax Cyllinder”)

(replace “with” with “matching” or “having” if you prefer)

I don’t love it, but like it much more than “tracksHavingMediaType”:

- still much more consistent about what goes into explicit parameters
- having a “with”/etc helps convey that parameters are the criteria for tracks returned
- doable as an automatic translation from ObjC

>> Ad 2: I can see why you don’t like “removeFirstTrack”. It sounds like
>> removing _the_ first track, rather than the first track that matches
>> criteria in parameters list. Perhaps a word like “Matching” would work
>> well to fix this concern. (And sounds/conveys intention better than
>> “with” or “having” IMHO)
> 
> There are contexts in which "matching" is more ambiguous than "having",
> e.g.
> 
>    x.trackMatchingMediaType(t) // track the matching media type?
> 
>    x.trackHavingMediaType(t)   // track is obviously a non-verb here.
> 
> Yes, I see how this relates to your "put back the verb" idea.
> 
>> 
>> Just my 2¢,
>> — Radek
>> 
>>> On 03 Feb 2016, at 01:32, Dave Abrahams via swift-evolution <swift-evolution at swift.org> wrote:
>>> 
>>> 
>>> This thread is related to the review of new API guidelines, but it's not
>>> a review thread; it's exploratory.  The goal is to come up with
>>> guidelines that:
>>> 
>>> * describe when and where to use argument labels
>>> * require labels in many of the cases people have asked for them
>>> * are understandable by humans
>>> * preserve important semantics communicated by existing APIs.
>>> 
>>> Here's what I'm thinking
>>> 
>>> 1. If and only if the first argument could complete a sentence*
>>>  beginning in the base name and describing the primary semantics of
>>>  the call, it gets no argument label:
>>> 
>>>    a.contains(b)  // b completes the phrase "a contains b"
>>>    a.mergeWith(b) // b completes the phrase "merge with b"
>>> 
>>>    a.dismiss(animated: b) // "a, dismiss b" is a sentence but 
>>>                           // doesn't describe the semantics at all, 
>>>                           // thus we add a label for b.
>>> 
>>>    a.moveTo(x: 300, y: 400) // "a, move to 300" is a sentence 
>>>                             // but doesn't describe the primary 
>>>                             // semantics, which are to move in both
>>>                             // x and y.  Thus, x gets a label.
>>> 
>>>    a.readFrom(u, ofType: b) // "a, read from u" describes
>>>                             // the primary semantics, so u gets no
>>>                             // label. b is an
>>>                             // option that tunes the primary
>>>                             // semantics
>>> 
>>>  [Note that this covers all the direct object cases and, I believe,
>>>  all the default argument cases too, so maybe that exception can be
>>>  dropped.  We still need the exceptions for full-width type
>>>  conversions and indistinguishable peers]
>>> 
>>>  Note: when there is a noun in the base name describing the role of the
>>>  first argument, we skip it in considering this criterion:
>>> 
>>>     a.addObserver(b) // "a, add b" completes a sentence describing 
>>>                      // the semantics.  "Observer" is omitted in 
>>>                      // making this determination.
>>> 
>>> * We could say "clause" here but I think making it an *independent*
>>> clause doesn't rule out any important use-cases (see
>>> https://web.cn.edu/kwheeler/gram_clauses_n_phrases.html) and at that
>>> point, you might as well say "sentence," which is a more
>>> universally-understood term.
>>> 
>>> 2. Words that describe attributes of an *already-existing* instance
>>>  should go in the base name rather than in a label:
>>> 
>>>     a.tracksHavingMediaType("Wax Cylinder")      // yes
>>>     a.removeFirstTrackHavingMediaType("BetaMax") // yes
>>> 
>>>     a.tracks(mediaType: "Wax Cylinder")          // no
>>>     a.removeFirstTrack(havingMediaType: "BetaMax") // no
>>> 
>>>  [yes, we could use "With" instead of "Having", but it's more
>>>  ambiguous]
>>> 
>>>  Words that describe attributes of an instance *to be created* should
>>>  go in argument labels, rather than the base name (for parity with
>>>  initializers):
>>> 
>>>     AudioTrack(mediaType: "BetaMax")                   // initializer
>>>     trackFactory.newTrack(mediaType: "Wax Cylinder")   // yes
>>> 
>>>     trackFactory.newTrackWithMediaType("Wax Cylinder") // no
>>> 
>>> 3. (this one is separable) When the first argument is the *name* or
>>>  *identifier* of the subject in the base name, do not label it or
>>>  describe it in the base name.
>>> 
>>>     a.transitionToScene(.GreatHall)               // yes
>>>     a.transitionToSceneWithIdentifier(.GreatHall) // no
>>> 
>>>     let p = someFont.glyph("propellor")           // yes
>>>     let p = someFont.glyphWithName("propellor")   // no
>>>     let p = someFont.glyph(name: "propellor")     // no
>>> 
>>> Thoughts?
>>> 
>>> -- 
>>> -Dave
>>> 
>>> _______________________________________________
>>> swift-evolution mailing list
>>> swift-evolution at swift.org
>>> https://lists.swift.org/mailman/listinfo/swift-evolution
>> 
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> 
> -- 
> -Dave
> 
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