[swift-evolution] [Guidelines, First Argument Labels]: Prepositions inside the parens

[Matthew Judge]

> On Feb 10, 2016, at 18:17, Dave Abrahams <dabrahams at apple.com> wrote:
> 
> 
>> on Wed Feb 10 2016, Matthew Judge <matthew.judge-AT-gmail.com> wrote:
>> 
>> On Tue, Feb 9, 2016 at 2:18 PM, Dave Abrahams via swift-evolution <
>> swift-evolution at swift.org> wrote:
>> 
>>> 
>>> Hi everybody,
>>> 
>>> Having looked at some examples, the API guidelines working group members
>>> that were present this morning agreed we really want prepositions inside
>>> the parentheses of method calls.
>>> 
>>> Here are some results for the importer; we're still tuning some of the
>>> heuristics but overall we feel very good about the preposition
>>> placement:
>>> 
>>> 
>>> https://github.com/apple/swift-3-api-guidelines-review/commit/da7e512cf75688e6da148dd2a8b27ae9efcb8821?diff=split
>>> 
>>> Note that this is not final wording, but here are the guidelines we're
>>> working with for first argument labels:
>>> 
>>> A. Try to form a grammatical phrase including the first argument and
>>>   describing the primary semantics at the call site.
>> 
>> I assume that A is intended to cover:
>> 
>> a.addObserver(b) // yes
>> a.add(observer: b) // no
> 
> I don't know what you mean by "cover." It isn't intended to assign the
> "yes/no" decision to those; they both form (the same) grammatical phrase
> at the call site.  The choice between those two is governed by B, below.

By cover I meant assign the "yes/no" decision. So because the first argument is part of the primary semantics, it doesn't get an argument label (per B.1) and the word observer needs to be in the base name so as not to change the semantic meaning.

> 
>> I believe I can read this behavior into A by inferring "a grammatical
>> phrase including [the base name and] the first argument" but I want to make
>> sure this is the intent.
>> 
>>> 
>>> B. The first argument gets a label when and only when:
>>> 
>>>   1. It does not form part of a grammatical phrase describing the
>>>      primary semantics.  For example,
>>>      ```
>>>      x.dismiss(animated: y)
>>>      ```
>>>      [more examples needed]
>>>      Note that parameters with defaults never describe the primary
>>>      semantics. so are always labeled.
>>>      ```
>>>      func invert(options options: SomeOptionSet = []) // yes
>>>      func invert(_ options: SomeOptionSet = [])       // no
>>>      ```
>>> 
>>>   2. The method is a factory method; such calls should mirror
>>>      initializers, with no preposition.  For example,
>>>      ```
>>>      let x = UIColor(red: r, green: g, blue: b)
>>>      let y = monitor.makeColor(red: r, green: g, blue: b)
>>>      ```
>> 
>> If rule B.2 didn't exist
>> 
>> let y = monitor.makeColor(red: r, green: g, blue: b)
>> 
>> would still have the first argument labeled by B.1 wouldn't it?
> 
> Yes, but you could have done this grammatically, as 
> 
>     let y = monitor.makeColorHavingRed(r, green: g, blue: b)
> 
> That's what B2 is designed to prevent.
> 
>> (Though without this rule, the guidelines wouldn't be clear on whether
>> or not to include prepositions in the argument labels.)
>> 
>>> 
>>>   3. It is part of a prepositional phrase
>>> 
>>>     a. The label normally starts with the preposition.
>>>        For example,
>>>        ```
>>>        x.move(from: a, to: b)
>>>        x.loadValues(forKeys: ["fox", "box", "lox"])
>>>        ```
>>>     b. ...unless the preposition would break a very tight association
>>>        between parameters:
>>>        ```
>>>        x.moveTo(x: a, y: b)
>>>        ```
>>>        [encourage grouping parameters into higher-level concepts,
>>>        e.g. Point, in these cases]
>> This seems clear and straightforward to apply. The only place where
>> this isn't totally clear is when there are multiple prepositions (as
>> highlighted in Jacob's response),
> 
> Multiple prepositions before the first argument?

Yes, before and including the first argument label. For example (from Jacob's response):

comparePositionInDecodeOrderWithPosition(of cursor: AVSampleCursor) -> ComparisonResult

Jacob suggests spelling it:

comparePositionInDecodeOrder(withPositionOf cursor: AVSampleCursor) -> ComparisonResult

I agree that Jacob's spelling is better, but not enough better to justify additional guidelines about prepositions.

> 
>> but I think B.3 provides the right level of guidance... much more
>> detail will start being too many guidelines and special cases.
> 
> Thanks!
> -- 
> -Dave