[swift-evolution] Extending trailing closure sugar similar to property accessors

[Eric Summers]

I’d like to hear thoughts on extending trailing closure syntax to avoid long inline closures.  A significant benefit to adopting this sugar would be to clarify indentation style for long inline closures.  I apologize if this has been brought up before, but I couldn’t find anything searching the list.

There is a lot of discussion about hacking around the issues with inline closures.  Here are a few examples:
https://www.natashatherobot.com/swift-trailing-closure-syntax/
https://owensd.io/2015/02/20/handling-multiple-closure-parameters/
https://bugs.swift.org/browse/SR-1199
https://lists.swift.org/pipermail/swift-evolution/Week-of-Mon-20160606/020470.html

I think a syntax similar to property accessors to allow multiple trailing closures could make these scenarios feel swifty.  Property accessors already have a "get" specialization that is similar to the current trailing closures syntax, so in theory this could be a backwards compatible extension. 

func foobar(a: Int, b: Int, completionBlock: ((Int, Int) -> Void), failureBlock: ((Int, Int) -> Void) {
    // ...
}
    
// Current syntax:
foobar(a: 1, b: 2,
    completionBlock: { x, y in
    // ...
    },
    failureBlock: { i, j in
    // ...
    })
    
// A sugar similar to property accessors for multiple trailing closures:
foobar(a: 1, b: 2) {
    completionBlock { x, y in
    // ...
    }
    failureBlock { i, j in
    // ...
    }
}

Best,
Eric

-------------- next part --------------
An HTML attachment was scrubbed...
URL: <https://lists.swift.org/pipermail/swift-evolution/attachments/20171102/e085f31a/attachment.html>