[swift-evolution] When to use argument labels (a new approach)

[Charles Constant]

I find arguments with prepositions easier to read, on the whole, even when
they're not strictly necessary.

Even though, this code makes sense:

*     a.move_to( b )*

*     draw_line( origin: b, conclusion: c )*

I'd prefer to see this:

*     a.move( to_point: b )*

*     draw_line( from_point: b, to_point: c )*

Similarly, for the example "*a.read_from( u, of_type: b )*" I find this
easier to read:

*     a.read( from_url: u, from_type: b)*

Which makes it easier to understand if it's followed by:


*     a.read( from_url: u, to_type: b)*

I find it helpful in my own code. Having said that, I'm not sure if it
would suit huge multi-person projects, since it leads to a lot of similarly
named functions.

On Tue, 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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> swift-evolution at swift.org
> https://lists.swift.org/mailman/listinfo/swift-evolution
>
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