[swift-evolution] [Proposal] Shorthand Argument Renaming

[Vladimir.S]

Personally I also don't like the `$N` syntax. But I don't suport `.N` 
syntax as it looks like the closure argument is tuple, and like we use 
tuple's values in body. But we removed association between tuples and 
function parameters in Swift.

First my thoughts were about `_1` `_2` syntax.

reversed = names.sort( { _0 > _1 } )

as `_` similar as unnamed variable/parameter like

let _ = something()

But I'm also not sure if it worth to change this

On 30.05.2016 19:44, Frédéric Blondiau via swift-evolution 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.
>
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