[swift-evolution] Guaranteed closure execution

[Gwendal Roué]

> Le 23 avr. 2016 à 15:47, michael.peternell at gmx.at a écrit :
> 
> why not just write
> 
>    func f(closure: @once () -> ()) // ?
> 
> Because, to be honest, I don't want to have to learn the difference between an "argument qualifier" and a "type attribute". 

I'm with you here, but I will certainly not fight a Swift lawyer about the actual syntax :-)

For me the best syntax is the following because it makes the @noescape explicit, so that I know that I don't need to use explicit `self.` inside the closure.

	func f(closure: @noescape(once) () -> ())

	let x: Int
	f { x = myIntProperty } // implicit self

> When I think of it, my experimental synchronized-function would also profit from '@once':
> 
>    /// same as Objective-C's @synchronized(object) { ... } function.
>    func synchronized<T>(lock: AnyObject, @noescape _ closure: () throws -> T) rethrows -> T {
>        var result: T;
>        objc_sync_enter(lock)
>        defer { objc_sync_exit(lock) }
>        result = try closure()
>        return result;
>    }

I'm glad you see the point :-) I really believe that @noescape(once) is on the same boat as SE-0061 "Add Generic Result and Error Handling to autoreleasepool() https://github.com/apple/swift-evolution/blob/master/proposals/0061-autoreleasepool-signature.md

Gwendal