Apple and the Swift community has settled on this style:
https://devforums.apple.com/message/1133616#1133616
> FWIW, we've recently decided to standardize on () -> Void
> (generally, () for parameters and Void for return types) across all of our
> documentation.
We still have a bunch of redeclarations of Dispatch functions to avoid
the automatic bridging of dispatch_data_t and dispatch_block_t, but
mostly this is a vast reduction in complexity (and increase in safety).
Adds an explicit @escaping throughout the standard library, validation
test suite, and tests. This will be necessary as soon as noescape is
the default for closure parameters.
* Fix DispatchSourceSignal initialisation such that it no longer
registers for the wrong source type.
* Remove (group:) option from DispatchWorkItem, introduce group
options to `.async` methods that accept DispatchWorkItem.
* Rename `DispatchSourceType` to `DispatchSourceProtocol`
* Rework DispatchQueue attributes and flags into a less confusing
approach.
* Fixes:
SR-1817, SR-1771, SR-1770, SR-1769
<rdar://problem/26725156> <rdar://problem/26873917>
<rdar://problem/26918843> <rdar://problem/26810149>
<rdar://problem/27117023> <rdar://problem/27121422>
<rdar://problem/27236887> <rdar://problem/27337555>
