[swift-evolution] When to use argument labels, part DEUX
matthew.judge at gmail.com
Sun Feb 7 07:11:31 CST 2016
> On Feb 7, 2016, at 00:31, Dave Abrahams via swift-evolution <swift-evolution at swift.org> wrote:
>> on Sat Feb 06 2016, plx <swift-evolution at swift.org> wrote:
>> I like these revisions quite a bit.
>>> On Feb 5, 2016, at 3:32 PM, Dave Abrahams via swift-evolution <swift-evolution at swift.org> wrote:
>>> Given all the awesome feedback I've gotten on this thread, I went back
>>> to the drawing board and came up with something new; I think this one
>>> works. The previously-stated goals still apply:
>>> * describe when and where to use argument labels
>>> * require labels in many of the cases people have asked for them
>>> * are understandable by humans (this means relatively simple)
>>> * preserve important semantics communicated by existing APIs.
>>> Please keep in mind that it is a non-goal to capture considerations we
>>> think have a bearing on good names (such as relatedness of parameters):
>>> it's to create simple guidelines that have the right effect in nearly
>>> all cases.
>>> A. When arguments can't be usefully distinguished from one another, none
>>> should have argument labels, e.g. min(x,y), zip(x,y,z).
>>> B. Otherwise,
>>> 1. At the call site, a first parameter that has no argument label must
>>> form part of a grammatical phrase that starts with the basename, less
>>> any trailing nouns.
>>> ^~~~~~~~~~~~~~~~~ trailing noun
>>> This phrase must have the correct semantic implications, so, e.g.
>>> a.dismiss(b) // no, unless a is really dismissing b
>>> a.dismissAnimated(b) // no, not grammatical
>>> a.dismiss(animated: b) // yes, using a label
>>> 2. If the first argument is part of a prepositional phrase, put the
>>> parenthesis immediately after the preposition.
>>> a.moveFrom(b, to: c)
>>> Thus, if words are required for any reason between the preposition
>>> and the first argument, they go into the first argument label.
>>> a.tracksWith(mediaType: b, composer: c)
>>> a.moveTo(x: 22, y: 99)
>>> a. I would recommend prepositions other than "with" in nearly all
>>> cases, but that's not the point of these rules.
>>> b. I can understand the aesthetic appeal of
>>> a.move(from: b, to: c)
>> I agree with the aesthetic and also not wanting to complicate the rules to cover it.
>> I also think this is a bad example, though, b/c in practice one would
>> *hope* that such calls would look more like:
>> container.move(element, from: currentIndex, to: destinationIndex)
>> …and whatnot;
> I don't understand how this one works. In most cases the call would
> have lots of redundancy:
> container.move(container[currentIndex], from: currentIndex, to: destinationIndex)
> ^^^^^^^^^ ^^^^^^^^^ ~~~~~~~~~~~~ ~~~~~~~~~~~~
> Why make the caller come up with the element value here?
>> I suspect that the `move(from:to:)` case may be getting strong
>> reactions in part b/c it’s actually an unusually-poorly-named method
>> to begin with.
>> Also, as these are just guidelines, in third party code we can deviate
>> from them (at our own peril, but we can...).
>>> but I believe it is not a clear enough improvement to justify
>>> additional complexity in the guidelines.
>>> 1. I'm not expecting these guidelines to make everybody optimally happy,
>>> all the time, but they shouldn't be harmful. Are there any cases for
>>> which they produce results you couldn't live with?
>>> 2. Are there any cases where you'd be confused about how to apply these
>> I do find some of the rules worded in ways that are hard to apply in
>> the presence of trailing nouns; I’m not sure the guidelines are strong
>> enough here to force the “right” outcome.
>> Consider this example:
>> // not-intended:
>> a.tracksWithMediaCharacteristic(b, composer: c)
>> …applying our guidelines:
>> - `tracks with media characteristic b` is a grammatical phrase
> I went through a series of thoughts on this:
> 1. I'm not sure it is grammatical (I'll have to consult with a
> 2. I understand why it sounds natural: this is the somewhat misleading
> result of using a single-character identifier in the example. It's like
> talking about a hypothetical "person A" and "person B". You wouldn't think
> "Person Joe" was grammatical.
> 3. Yeah, but "umbrellas with color yellow" is perfectly fine, if
> slightly unnatural, and it has the same grammatical structure. My
> wife points out that it's like something you would say in poetry to
> make rhyme or meter work.
> 4. Again I need to consult with a linguist, but I now have hope that it
> actually is grammatical, meaning the whole “skipping trailing nouns
> on the base name” wrinkle can be eliminated from the guidelines.
>> - `tracks with b` is (arguably also) a grammatical phrase
> Yes, this was the interpretation for which I introduced the “skipping
> trailing nouns on the base name” wrinkle.
>> - `b` is “part of” the "noun phrase" "tracks with media characteristic
>> - `b` is “part of” the “prepositional phrase” “with media characteristic b"
> All true.
>> …and although I think this is fine under a “strict” application of the
>> guidelines—as `b` is part of a prepositional phrase, we *must* split
>> the base name after the preposition, at which point we are allowed to
>> “restore" the `mediaCharacteristic:` label if we wish
> I don't think of it as "restoring." It's simply that the phrase you're
> encoding is "tracks with media characteristic b" and b is part of a
> prepositional phrase, so you put a parenthesis after the preposition:
> "tracks with (media characteristic b"
> and then you apply camel case and everything falls into place.
>> —I don’t know in practice that the “strict” interpretation will be
>> what people naturally opt to use.
> Well, that's the intention of the guideline. I think if we give people
> examples to follow they will understand, but no matter *how* we phrase
> the guidelines there's always the risk that some people will choose to
> interpret them in unintended ways.
>> Taking it from the other direction, the way the guidelines are phrased
>> I worry bit that you wind up with:
>> // not intended
>> a.add(subview: v) (or add(v)) // instead of `a.addSubview(v)`
> That's allowed as the guidelines were originally posted, but with the
> modification to the guidelines that form B1 is to be preferred over form
> B2 when both are allowed... which I swore I posted something about in
> this thread in response to an excellent point someone made, but now
> can't find.
> Maybe I dreamt it; until I hear otherwise, *you* get credit for making
> the excellent point :-)
It was in response to my email, which I accidentally replied back only to you and not the list, so I'm the only one who saw your proposed modification. (Unfortunately I noticed that the list was not there after I replied a couple more times as well.)
>> a.add(layoutGuide: g) (or add(g)) // instead of `a.addLayoutGuide(g)`
>> a.add(gestureRecognizer: r) (or add(r)) // instead of
>> …b/c the rule that we should ignore such trailing nouns means those
>> are *exactly* as-grammatical as the “intended” imports (it’s “add v”
>> vs “add v”, after all, under the guidelines), so at least within the
>> proposed guidelines there’s no apparent reason to prefer the
>> `addSubview` form vis-a-vis the `add(subview:)` (or `add(_)`) form(s).
>> Perhaps I just overlooked something from the non-label guidelines in
>> this response, but it’d seem the omit-needless-words would also steer
>> you towards `add()`, with or without a first-argument label.
> It might appear to, but the words are very much needed in this case
> because adding a gesture recognizer is not the same kind of operation as
> adding an observer or subview.
>> So overall these guidelines seem more than adequate to resolve
>> labeling disputes if we are already dealing with "well-named”
>> functions but may be a bit weak to steer naming *decisions*.
> The guidelines in this particular thread are just trying to deal with
> the labels .
>> But, for guidelines, that might still be OK?
> Not because they're guidelines, but because of the scope of what we're
> trying to address here.
>>> Thanks in advance for all your valuable input!
>>> P.S. Doug is presently working on generating new importer results, based
>>> on these guidelines, for your perusal. They should be ready soon.
>>> swift-evolution mailing list
>>> swift-evolution at swift.org
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