[swift-evolution] [Pitch] Clarify behavior of comments near operators

Jesse Rusak me at jesserusak.com
Mon Dec 28 10:49:30 CST 2015

> On Dec 22, 2015, at 1:39 PM, Jordan Rose <jordan_rose at apple.com> wrote:
>> On Dec 21, 2015, at 19:23, Jesse Rusak <me at jesserusak.com <mailto:me at jesserusak.com>> wrote:
>>> On Dec 21, 2015, at 3:18 PM, Jordan Rose <jordan_rose at apple.com <mailto:jordan_rose at apple.com>> wrote:
>>> After looking at all your examples, I think I prefer "comments are not there" with a possible "multi-line comments are treated like newlines" extension. But either way I think having an actual model here and sticking to it is an improvement!
>> Thanks for your thoughts! To be clear, are you suggesting “comments are not there” for the purposes of whitespace near operators, or as part of a more-general rule to be applied everywhere? (i.e. do you mean the first or second of the alternatives I listed?)
> I'm not sure how your two alternatives map to these options, but I think the model I like has
> foo/*abc*/!
> as a postfix '!'. I'm not sure if I want to count
> foo/*abc
> */+ bar
> as an infix '+', as an error, or as a de-facto line continuation mechanism (making a postfix '+'). I do agree it's important to pick something.

I’ve spent some more time thinking about this. I think that “comments are whitespace” is a simpler model, but I do think it’s more surprising for many people, and (as Chris pointed out earlier) is less flexible, since you can always add whitespace next to a comment if you want it. So, I think I’m coming around to the “comments are not there” behavior. 

For your latter example, my feeling is that having the *content* of a comment affect the parsing of the surrounding code (i.e. treating your last example as an error or infix +) is surprising. For example, it would surprise me that this works:

a+/* something */b

but this doesn’t:

a+/* something 
       something */b

So, I think I’ll write up a draft proposal with the “comments are not there” behavior and see how it looks.

- Jesse
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