[swift-evolution] [Proposal] Automating Partial Application via Wildcards

[Craig Cruden]

There are things in Scala that flummoxed me early on - the underscore is not one of them.  It is just new syntax - similar to using $0 or something else that if you have not seen before or know what it is used for it throws you to begin with.  

It can always be taken to the extreme in a straw man argument to make a point, but for me it was definitely not an issue.




> On 2016-02-03, at 2:42:44, Matthew Johnson via swift-evolution <swift-evolution at swift.org> wrote:
> 
> 
>> On Feb 2, 2016, at 1:31 PM, Joe Groff <jgroff at apple.com <mailto:jgroff at apple.com>> wrote:
>> 
>> 
>>> On Feb 2, 2016, at 11:14 AM, Matthew Johnson <matthew at anandabits.com <mailto:matthew at anandabits.com>> wrote:
>>> 
>>> I know there is concern about overloading the semantics of `_` which is unfortunate as IMO it is the best symbol to serve as a placeholder.  I wonder if there has been confusion about the semantics in practice in languages like Scala where it is used in both ways.  Is there any evidence that this has been a problem?
>> 
>> Not a super scientific study, but if you google "scala underscore", several of the results on the first page indicate confusion or bewilderment:
>> 
>> Scala _ [underscore] magic · Anantha Kumaran <https://www.google.com/url?sa=t&rct=j&q=&esrc=s&source=web&cd=1&ved=0ahUKEwj-08ju59nKAhWj26YKHRuVBh8QFggdMAA&url=http%3A%2F%2Fananthakumaran.in%2F2010%2F03%2F29%2Fscala-underscore-magic.html&usg=AFQjCNEbIIoppVNYAjr6wqxL4byR9I1fAw&sig2=Hlw6hEFfsPqvlDvEFaDoyQ>
>> 
>> What are all the uses of an underscore in Scala? - Stack ... <https://www.google.com/url?sa=t&rct=j&q=&esrc=s&source=web&cd=2&ved=0ahUKEwj-08ju59nKAhWj26YKHRuVBh8QFggjMAE&url=http%3A%2F%2Fstackoverflow.com%2Fquestions%2F8000903%2Fwhat-are-all-the-uses-of-an-underscore-in-scala&usg=AFQjCNHVNCJVosr0IzZYmh8pJRdnXTnf6g&sig2=vqWgzaddf2kEkWrdgFQuoQ&bvm=bv.113034660,d.dGY>
>> 
>> Scala dreaded underscore - SlideShare <https://www.google.com/url?sa=t&rct=j&q=&esrc=s&source=web&cd=3&ved=0ahUKEwj-08ju59nKAhWj26YKHRuVBh8QFggqMAI&url=http%3A%2F%2Fwww.slideshare.net%2Fnormation%2Fscala-dreaded&usg=AFQjCNEs5fGA4e8NsU10--FKfOyga8aEaA&sig2=mlWWAnJgFVxSpA4UtA2wyw>
>> 
>> underscore confusion | The Scala Programming Language <http://www.scala-lang.org/old/node/2916.html>
>> 
> 
> Interesting.  It looks like Scala takes this to a crazy extreme.  I can definitely see why the core team is cautious about avoiding this mistake.  
> 
> The example in the last link you shared is a pretty strong argument for avoiding partial application syntax (regardless of placeholder).  It took me a minute to see what was happening there, while it would have been immediately clear with closure braces.
> 
> The thing I like about _ as a placeholder is the visual whitespace it leaves.  It looks like a “hole” in the expression.  I wish there was some other unclaimed symbol with that attribute.  
> 
> It would be nice if we could find something better than $.  The best argument in favor of that is precedent in other languages, but it comes at the cost of being noisy enough to impede readability IMO.
> 
> -Matthew
> 
>> -Joe
> 
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