[swift-evolution] Code blocks and trailing closures

[David Rönnqvist]

Xcode can already draw boxes for nesting scopes, but it’s disabled by default. You’ll find it under: Editor > Code Folding > Focus Follows Selection.

That said, IIRC it’s been mentioned on this list that (I’m paraphrasing) we should try and avoid designs that rely on editor functionality, and also that a Xcode is independent from the mailing list.


> On 20 Mar 2017, at 07:22, Rick Mann via swift-evolution <swift-evolution at swift.org> wrote:
> 
> I actually don't like this situation, either. I find it gets a bit confusing to know what's a block and what's just nested scope. I, too, have had an impulse to have a different keyword for returning from a block, but what I really want is for the entire scope of the block to be called out differently.
> 
> This is true regardless of whether or not it's a trailing closure.
> 
> I wonder if the source editor (e.g. Xcode) could draw three sides of a box with arrows:
> 
>    {                         <--------------------+
>        some code                                  |
>        more code                                  |
>    }                         <--------------------+
> 
> I don't know if this would quickly get messy and distracting. It would be challenging to find exactly the right way to draw it that pleases everyone (it should, obviously, be hyper-customizable, but Apple hates settings), and to draw it to make it easy to see what it's pointing to without trampling over end-of-line comments.
> 
> Maybe subtle highlighting of the background (all the way across the window) to show block, but that makes it harder to show nested blocks.
> 
> 
>> On Mar 19, 2017, at 20:33 , Kenny Leung via swift-evolution <swift-evolution at swift.org> wrote:
>> 
>> I have proposed that a different keyword be used to return out of blocks. In Objective-C, I have a #define that aliases “blockreturn” and I use that exclusively in breaking out of blocks.
>> 
>> -Kenny
>> 
>> 
>>> On Mar 15, 2017, at 3:35 AM, Rien via swift-evolution <swift-evolution at swift.org> wrote:
>>> 
>>> What does the following code fragment do?
>>> 
>>> serverCert.write(to: certificateUrl) { showErrorInKeyWindow(message); return }
>>> 
>>> The only possible answer is: I don’t know.
>>> 
>>> The problem is finding out what the “return” statement will do.
>>> 
>>> Without knowing if the {...} is a code block or a trailing closure it is impossible to know what the return statement will do. It will either end the closure or it will end the function that contains this code block.
>>> 
>>> This could be disambiguated by using the same syntax as for lazy variables:
>>> 
>>> serverCert.write(to: serverCertificateUrl) { showErrorInKeyWindow(message: message); return }()
>>> 
>>> Now it is clear that the return statement will only terminate the (trailing) closure.
>>> 
>>> A question to the educators on the list: Is this a real problem?
>>> 
>>> Personally, I dislike this situation, but I am also ambivalent towards the solution I just described.
>>> 
>>> Regards,
>>> Rien
>>> 
>>> Site: http://balancingrock.nl
>>> Blog: http://swiftrien.blogspot.com
>>> Github: http://github.com/Balancingrock
>>> Project: http://swiftfire.nl
>>> 
>>> 
>>> 
>>> 
>>> 
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>>> https://lists.swift.org/mailman/listinfo/swift-evolution
>> 
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> 
> 
> -- 
> Rick Mann
> rmann at latencyzero.com
> 
> 
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