[swift-evolution] When to use argument labels, part DEUX (was: when to use argument labels (a new approach))

Daniel Steinberg daniel at dimsumthinking.com
Sat Feb 6 09:50:39 CST 2016

Thanks for this Dave - I really like this document.

I had a few nits but spent a day away from it and came back and think that this codifies much of what I’d love to see and I’d be happy following it.

What I particularly like is that it presents APIs from the perspective of the caller.

I don’t know if the following is part of this proposal, but I think one thing that might helpfully be discussed is how we refer to these methods when speaking or writing about them. To me this only matters in methods where there are argument labels - but it matters.

For example, in Objective-C, the selector would make it easy for us to agree that the method name is moveFrom:to:. How do we refer to moveFrom(a, to: b)? Is it the moveFrom method? This also helps me care less whether it is moveFrom(a, to: b) or move(from:a, to: b)  - I too prefer the second version but not enough to object and not at all if the “to" is part of how we refer to this method.

Thoughts? Or is that out of scope?



> On Feb 5, 2016, at 4:32 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.  
>       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
> _______________________________________________
> swift-evolution mailing list
> swift-evolution at swift.org
> https://lists.swift.org/mailman/listinfo/swift-evolution

More information about the swift-evolution mailing list