[swift-evolution] Lambda function syntax

[Alexander Regueiro]

The standard map syntax is directly inspired by that of C#.

For Swift, I’d be relatively happy with something like the following (repeating what’s already been said I believe)

map ({ x => x + 5 })

or using trailing closure

map { x => x + 5 }

with the possibility of an additional single-line option:

map ( x => x + 5 )

(which is useful in the case of non-trailing-closure expressions).

Of course, I’d rather remove trailing closures altogether, but I suspect that won’t happen. :(

> On 23 Dec 2015, at 03:45, Craig Cruden <ccruden at novafore.com> wrote:
> 
> It has probably been 6 months since I have had time to do anything interesting (JDK6 + Oracle SQL recently for contracts recently) so if I am messing up terminology or syntax - please excuse me.  I messed a few things up and had to open up an old Scala project to remind me what I was doing.
> 
> 
> The standard map syntax for Scala is:
> 
> 	a.map(x => x + 5)
> 
> or using a placeholder (very limited shorthand - cannot use a placeholder twice for the same value):
> 
> 	a.map(_ + 5)
> 
> if it is a tuple then
> 
> 	a.map(x => f(x._1, x._2))
> 
> or you can pass in a function block (with pattern matching case)
> 
> 	a.map { case (x, y) => (y, x) }
> 
> there might be some mathematical reason behind the “in” keyword - but it is lost on me as well (it has been a good 30 years since University) and gets lost on me.  If I had more time I might get use to it.
> 
> I hope I did not mess up those examples as bad.
> 
> 
>  
> 
>> On 2015-12-23, at 9:52:46, Andrey Tarantsov <andrey at tarantsov.com <mailto:andrey at tarantsov.com>> wrote:
>> 
>>> foo.map( bar => bar.boz) // single line
>> 
>> Well how important is it to use () instead of {} here?
>> 
>> If you make it
>> 
>> foo.map { bar => bar.boz }
>> 
>> then it's like it is now, but with "in" replace by "=>".
>> 
>>> foo.map { (x, y) => x * 5 + y }
>> 
>> I actually like the bare version:
>> 
>> foo.map { x, y => x * 5 + y }
>> 
>> but not in your example (here it looks atrocious). Take this real code, though:
>> 
>> 
>>         constrain(topBlock, tableView, view) { top, tbl, sup in
>>             top.left  == sup.left + horizPadding
>>             top.right == sup.right - horizPadding
>>             top.top   == sup.top  + topPadding
>> 
>>             tbl.top    == top.bottom + 16
>>             tbl.bottom == sup.bottom
>> 
>>             tbl.left  == sup.left + horizPadding - horizTableHang
>>             tbl.right == sup.right - horizPadding + horizTableHang
>>         }
>> 
>> I think the lack of parens is beneficial in reducing the visual noise here.
>> 
>>> And yes, I certainly would prefer `=>` rather than `in`.
>> 
>> It seems like the community can actually agree on this.
>> 
>> Does anyone know if it has any parsing problems / grammar implications right now? 
>> 
>>> I think a big problem with `in` is that it’s textual, and doesn’t provide a clear visual separation from keywords/names at the start of the body or the end of the type specifier.
>> 
>> Yes, agreed. “Not delimited enough”.
>> 
>>> (Are the [parentheses] around `bar` in your example required? I’m ambivalent to them.)
>> 
>> No, they are not, as shown above.
>> 
>>> To be clear, I’m still not a fan of the Ruby syntax. I think it makes the parsing easier for a compiler but harder for a human…
>> 
>> Depends on the human. To this specific human, the Ruby-style one is the easiest to parse (and mind you, I had very limited experience with Ruby compared to other languages, so it's not just being used to it, but rather an honest love and preference).
>> 
>> A.
>> 
> 

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