[swift-evolution] [Pitch] Support for pure functions. Part n + 1.

[Matthew Johnson]

How do you suggest a closure indicate its purity? Something like this?  

{ pure in $0.property } 

> On Feb 17, 2017, at 10:57 AM, Florent Vilmart <florent at flovilmart.com> wrote:
> 
> We were discussing the topic yesterday with others and some suggested adding a pure keyword, for improved readability, just before the function declaration:
> 
> Ex:
> 
> pure func(a:Some) -> Else {}
> 
> 
> 
> On Feb 17, 2017, 11:51 AM -0500, Matthew Johnson via swift-evolution <swift-evolution at swift.org>, wrote:
>> 
>>> On Feb 17, 2017, at 10:46 AM, David Sweeris via swift-evolution <swift-evolution at swift.org <mailto:swift-evolution at swift.org>> wrote:
>>> 
>>> 
>>> On Feb 17, 2017, at 08:21, Adrian Zubarev via swift-evolution <swift-evolution at swift.org <mailto:swift-evolution at swift.org>> wrote:
>>> 
>>>> I haven’t yet read all the feedback in this topic but I’d like to throw some bikeshedding of mine into the room. :)
>>>> 
>>>> How about this?
>>>> 
>>>> Version 1: func(pure) …
>>>> Version 2: func label(…) ~> ReturnType
>>> Version 2 is going to upset those who use "~>" as an operator.
>>> 
>>> As the # of possible attributes grows, having an obvious grouping mechanism for them, like version 1, might be worthwhile simply to help make the list clearer. What about allowing "@(list, of, attributes)" instead of "@list, @of, @attributes”?
>> 
>> That would be a little bit awkward for attributes that are parameterized.  And if we did do this we should allow the parens to be omitted when there is only one attribute.
>> 
>>> 
>>> - Dave Sweeris
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