A defer keyword in Swift

DeferredTaskList.swift

//
//  defer.swift
//  DeferredTaskList
//

private class DeferredTasks
{
  private typealias Task = () -> ()
  var list = [Task]()

  deinit
  {
    for task in list.reverse()
    {
      task()
    }
  }
}

struct Deferred
{
  private var d = DeferredTasks()

  init() { }

  init(_ task: () -> ())
  {
    d.list.append(task)
  }

  init<IgnoredType>(task: () -> IgnoredType)
  {
    d.list.append { _ = task() }
  }

  func defer(task: () -> ())
  {
    d.list.append(task)
  }

  func defer<IgnoredType>(task: () -> IgnoredType)
  {
    d.list.append { _ = task() }
  }
}


private func test()
{
  var T = Deferred {println("last thing to happen.")}

  var f1 = "fileref 1"
  T.defer {println("close " + f1)}
  println(f1 + " is ready for use")

  var f2 = "fileref 2"
  T.defer {println("close " + f2)}
  println(f2 + " is ready for use")

  println("do things with " + f1 + " and " + f2)
}

test()

A simple way to do in swift something similar to go's defer statement.
Difference: it's a closure being passed, so context is carried. Go's defer is somewhat like a pause between function parameter evaluation and function execution.

The trick is to use the deinitializer to trigger the execution of a list of closures.

The output of test() is as follows:

fileref 1 is ready for use
fileref 2 is ready for use
do things with fileref 1 and fileref 2
close fileref 2
close fileref 1
last thing to happen.