[swift-evolution] Removing "_ in" from empty closures

David Sweeris davesweeris at mac.com
Fri May 13 11:16:54 CDT 2016

+1, provided it doesn't make life difficult for the compiler.

Sent from my iPhone

> On May 13, 2016, at 11:13, Rob Napier via swift-evolution <swift-evolution at swift.org> wrote:
> Currently if a closure takes a value, it requires "_ in" to note that the value is ignored. This makes sense in many cases, but creates a bit of a mess in the case of an empty, void-returning closure:
> doThing(withCompletion: { _ in })
> I'd like to suggest that the compiler promote the empty closure literal {} to any void-returning closure type so that this could be written:
> doThing(withCompletion: {})
> This encourages the use of empty closures over optional closures, which I think is open for debate. In general I try to avoid optionals when they can be precisely replaced with a non-optional value. Furthermore, most Cocoa completion handlers are not optional.
> The alternative is to not do this, but encourage that any closure that could reasonably be empty should in fact be optional. I would then want Cocoa functions with void-returning closures to be imported as optionals to avoid "{ _ in }".
> -Rob
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