[swift-evolution] Code blocks and trailing closures

[Rick Mann]

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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> 
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-- 
Rick Mann
rmann at latencyzero.com