[swift-evolution] When to use argument labels (a new approach)
Dave Abrahams
dabrahams at apple.com
Wed Feb 3 17:54:44 CST 2016
on Wed Feb 03 2016, Charles Kissinger <swift-evolution at swift.org> wrote:
>> On Feb 3, 2016, at 2:06 PM, Dave Abrahams via swift-evolution
>> <swift-evolution at swift.org> wrote:
>
>>
>>> The “sentence” requirement of Rule 1 doesn’t seem to be met here, but
>>> the “primary semantics” part would still apply?
>>
>> I don't know what you mean; AFAICT, both parts apply; you have to apply
>> them together. You omit the argument label if and only if you can
>> describe the primary semantics with a complete sentence starting in the
>> base name and ending in the first argument. The primary semantics of
>> the method don't end with the mediaType: the genre is as much part of
>> the primary semantics, so we use an argument label.
>
> What I was getting at there is that
> ‘a.tracksHavingMediaTypeWaxCylinder’ doesn’t seem like a sentence to
> me. It is a clause, no doubt, but doesn’t seem to be an independent
> one.
Agh, you're right. If only we used verbs in these cases... but that is
a whole nother discussion. I guess I'll have to say "clause" instead of
"sentence," which really sucks. Or I can say there's an implied "get"
at the front if there's no verb. bleah.
> It was unclear to me whether it didn’t fit the Rule 1 criteria for
> that reason, but Rule 2 was specifically including it, or whether I
> just wasn’t seeing the “sentence-like” nature of it.
>
> —CK
>
>>
>>> —CK
>>>
>>>> On Feb 2, 2016, at 4:32 PM, 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
>>>>
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>>>
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>>
>> --
>> -Dave
>>
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--
-Dave
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