import Foundation
import PlaygroundSupport
 
class TestObject {
    let name: String
    
    init(name: String) {
        self.name = name
    }
}
 
class Runner {
    let dispatchQueue = DispatchQueue(label: "Playground.TestQueue", qos: .background)
    let objects: [TestObject]
    
    init(objects: [TestObject]) {
        self.objects = objects
    }
    
    func run() {
        self.objects.forEach({ (object) in
            //: I expect this syntax to work, weakfying the `object` variable before passing to the block,
            //: but it actually causes the compiler to crash with error "Segmentation fault: 11"
            self.dispatchQueue.async { [weak object] in
                print(object?.name ?? "<Nil object>")
            }
            
            //: Weirdly, if you uncomment the code bellow the compiler will stop crashing! :)
            //weak var _: TestObject? = object
        })
    }
}
let runner = Runner(objects: [TestObject(name: "a"), TestObject(name: "b"), TestObject(name: "c"), TestObject(name: "d")])
runner.run()
 
PlaygroundPage.current.needsIndefiniteExecution = true