Marking a variadic closure parameter as escaping

Question

Assuming a @nonescaping variadic closure parameter as in

func method(_ closures: () -> Void...)

then mutating it to @escaping as in

func method(_ closures: @escaping () -> Void...)

produces the following error.

@escaping attribute may only be used in function parameter position

https://stackoverflow.com/a/29750368/7880059 may be the answer. — , Jan 15 '18 at 16:51
`func method(_ closures: [@escaping () -> Void])` produces the same error as of Swift 4. — , Jan 15 '18 at 16:55
It’s a compiletime error. As far as I can see `@escaping` and `@autoclosure` are exclusively supported by the function type. _Edit: I was replying to Özgür Ersil’s now deleted comment._ — , Jan 15 '18 at 17:04

score 4 · Accepted Answer · answered Jan 15 '18 at 17:10

You don't need to use @escaping here at all. Only a closure that is directly an argument (with nothing wrapping it) can be non-escaping.

A closure that is part of a variadic argument is (under the hood) wrapped in an Array, so it is already implicitly @escaping.

For example, this compiles and runs just fine:

class MyObject {

    var closures: [() -> ()] = []

    func add(_ closures: () -> () ...) {
        self.closures += closures
    }

    func run() {
        for closure in closures { closure() }
    }

}

let object = MyObject()
object.add({ print("first") }, { print("second") })
object.run()

Marking a variadic closure parameter as escaping

1 Answers1