[swift-evolution] [Proposal] Shorthand Argument Renaming

[David Waite]

Not for or against a change in shorthand/defaulted names in general, but leading-dot in particular.

Leading dot already means something (access a static property/method of the expected type, including enum types). This usage has nothing to do with that existing behavior of the syntax other than being terse. Reusing syntax for wildly different behavior is also a recipe for confusion.

In addition, the dot syntax may make people think they are acting on a member of a type or tuple, while that is not currently the underlying behavior.

-DW

> On May 30, 2016, at 12:44 PM, Frédéric Blondiau via swift-evolution <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

-------------- next part --------------
A non-text attachment was scrubbed...
Name: signature.asc
Type: application/pgp-signature
Size: 496 bytes
Desc: Message signed with OpenPGP using GPGMail
URL: <https://lists.swift.org/pipermail/swift-evolution/attachments/20160601/621f3d2b/attachment.sig>