[swift-evolution] [Pitch] Move @noescape

[Chris Lattner]

> On Mar 3, 2016, at 2:14 PM, Jacob Bandes-Storch <jtbandes at gmail.com> wrote:
> 
> Will this allow me to write "let myDispatchSync = dispatch_sync as! @noescape () -> Void"  ? :-D

Yes,  but you need to spell it like this:

	let myDispatchSync = dispatch_sync as! ((dispatch_queue_t, @noescape @convention(block) () -> ()) -> Void)

The right answer here is to add @noescape to the imported symbol of course.

-Chris


> Sounds good to me, the old syntax is not necessary anymore.
> 
> Jacob
> 
> On Thu, Mar 3, 2016 at 2:01 PM, Chris Lattner via swift-evolution <swift-evolution at swift.org <mailto:swift-evolution at swift.org>> wrote:
> Chris Eidhof noticed an emergent result of removing our currying syntax: it broke some useful code using @noescape, because we only allowed it on parameter declarations, not on general things-of-function-type.  This meant that manually curried code like this:
> 
> func curriedFlatMap<A, B>(x: [A]) -> (@noescape A -> [B]) -> [B] {
>     return { f in
>         x.flatMap(f)
>     }
> }
> 
> Was rejected.  Fixing this was straight-forward (https://github.com/apple/swift/commit/c3c6beac72bc0368030f06d52c46b6444fc48dbd <https://github.com/apple/swift/commit/c3c6beac72bc0368030f06d52c46b6444fc48dbd>), but required @noescape being allowed on arbitrary function types.  Now that we have that, these two declarations are equivalent:
> 
>         func f(@noescape fn : () -> ()) {}
>         func f(fn : @noescape () -> ()) {}
> 
> I propose that we remove the former syntax, migrating code to the later form.  This leads to better consistency between our declarations and types, and follows the precedent of inout.  @autoclosure should also probably move as well.
> 
> Thoughts?
> 
> -Chris
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