[swift-evolution] When to use argument labels, part DEUX

Dave Abrahams dabrahams at apple.com
Fri Feb 5 16:05:03 CST 2016

on Fri Feb 05 2016, David Hart <swift-evolution at swift.org> wrote:

> Hello Dave,
> This is really shaping up nicely. Unfortunately, I still have difficulties with:
> a.moveFrom(b, to: c)
> I understand the need to have simply guidelines, but this just reads
> wrong to me, especially because b and c have equal importance. This is
> so much better IMHO:
> a.move(from: b, to: c)

Again, I understand the aesthetic preference for this form; I even
prefer it myself.  On the other hand, it seems to me that the difference
between the two forms reflects a point of emphasis that isn't crucial to
understandability at the use-site.  That's why I'm asking whether you
*can't live with* the results.  Are you merely expressing a strong
preference, or are you saying the first form is too awful to abide?

> But I’m not sure how to write a simple rule to explain this reasoning.

Any *additional* rule is more complexity in the guidelines, which would
have to pay for itself in some objective terms.  Since (I'm assuming
you'll agree that) it doesn't make a difference to understandability,
what objective criteria would you use to justify accomodating cases like

> David.
>> On 05 Feb 2016, at 22:32, 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.  
>>       print(x)
>>       a.contains(b)
>>       a.mergeWith(b)
>>       a.addGestureRecognizer(x)
>>            ^~~~~~~~~~~~~~~~~ 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.encodeWith(b)
>>       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)
>> Notes: 
>> 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)
>>   but I believe it is not a clear enough improvement to justify
>>   additional complexity in the guidelines.
>> Questions:
>> 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
>>   guidelines?
>> 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.
>> -- 
>> -Dave
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