[swift-evolution] [Proposal] Shorthand Argument Renaming

[Chris Williams]

Honestly what I’ve wanted for quite some time is just reasonable default parameter names. $0/$1… or any variation on index-based arguments is terrible for comprehension, and I feel like I’m being lazy and hurting whoever has to look at the code next every time I type out something like say <A [String: String]?.map { $0 } instead of .map{ key, value in key }. If the Dictionary type’s map function could define “key” and “value” as parameter types it would go a long way in terms or readability, in my opinion.

The index-based shorthand is rough to skim if you’re not well versed in the types your dealing with a a given time.

> Thanks for your feedback.
> 
> I personally never found that this “$n” convention was “Swift-like”... but it’s true that a “$n” is easier to spot than a “.n”, and I got used to also.
> 
> However, I realised how much this was disturbing for newcomers, when explaining closure shorthand argument names to a classroom of computer science students (aged 21) discovering Swift.
> 
> The feedback some gave me, during the course, was quite surprisingly strong and negative about this “$n” convention. This convinced me to write this proposal : for newcomers, the “$n” zero-based is something wrong.
> 
> I understand that association between tuples and function parameters in Swift is to be removed, but, in this case, as we have no parameters at all, I thought this was a distinct enough situation.
> 
> As suggested, considering this is a kind of compiler magic, using #0, #1 instead, may indeed be a better alternative.
> 
> I’m still waiting some feedback before writing an official proposal.
> 
> > On 30 May 2016, at 19:12, Leonardo Pessoa<me at lmpessoa.com>wrote:
> > 
> > Fréderic, the idea and reasoning are good and do make sense but I'm
> > not 100% go on this. When I started using this syntax I felt like I
> > was back in PHP but once I got used it's ok. I don't see anything
> > wrong that justifies the change in syntax. Looking at your examples I
> > even think it's easier to spot "$n" in my code than ".n".
> > 
> > 
> > On 30 May 2016 at 13:44, Frédéric Blondiau<swift-evolution at swift.org>wrote:
> > > Hello,
> > > 
> > > I was thinking about this, and would like to get some feedback before making my first proposal.
> > > 
> > > Best regards,
> > > 
> > > 
> > > Fred.
> > > ---
> > > 
> > > Shorthand Argument Renaming
> > > 
> > > 
> > > Introduction
> > > 
> > > Swift automatically provides shorthand argument names to inline closures which cleverly allows us to write
> > > 
> > > reversed = names.sort( { $0>$1 } )
> > > 
> > > I would suggest to use another syntax, using these new “names”
> > > 
> > > reversed = names.sort( { .0>.1 } )
> > > 
> > > 
> > > Motivation
> > > 
> > > The $n notation is generally used with positional parameters using one-based numbering, $1 referring to argument 1; $2, to argument 2... with a special meaning for $0 (could be the name of the function, or the full list of parameters).
> > > 
> > > This $n notation is often handy, but feels strange in Swift... like imported from UNIX scripting (but here zero-based, anyway).
> > > 
> > > 
> > > Proposed solution
> > > 
> > > The .n notation is more Swift-like — as used to access Tuple members, for example.
> > > 
> > > 
> > > Detailed design
> > > 
> > > Today, .0 or .1 (as any .n's) are refused by the compiler, as being not valid floating point literals.
> > > 
> > > I’m not a compiler expert, but eventually fetching this error inside a closure body could easily be translated into accepting this new syntax.
> > > 
> > > There can’t be conflict with other shorthands (like accessing static members using dot notation) as members can’t consist of only digits characters.
> > > 
> > > 
> > > Impact on existing code
> > > 
> > > $n need to be rewritten .n
> > > 
> > > 
> > > Alternatives considered
> > > 
> > > Create a default argument named “arguments” (like “error” in catch, “newValue” in setters or “oldValue” in a a didSet observer) accessed like a Tuple
> > > 
> > > reversed = names.sort( { arguments.0>arguments.1 } )
> > > 
> > > but this is (of course) much less convenient.
> > > 
> > > _______________________________________________
> > > swift-evolution mailing list
> > > swift-evolution at swift.org
> > > https://lists.swift.org/mailman/listinfo/swift-evolution
> 
> 
>