@inline(never)
func highLevel() {
  var collected: [[Entry]] = []
  var stack: [State] = []

  for i in 0 ..< 100_000 {
    var state = State(payload: .init(start: i, end: i + 1))
    for j in 0 ..< 100 {
      state.children.append(.init(payload: j ..< j + 1))
    }

    stack.append(state)
  }

  for i in 0 ..< stack.count {
    collected.append(stack[i].children)
    stack[i].children = []
  }

  let flatten = collected.flatMap { $0 }

  print(flatten.count)
}


@inline(never)
func unsafe() {
  var collected: [UnsafeMutableBufferPointer<Entry>] = []
  var stack: [State] = []

  for i in 0 ..< 100_000 {
    var state = State(payload: .init(start: i, end: i + 1))
    for j in 0 ..< 100 {
      state.children.append(.init(payload: j ..< j + 1))
    }

    stack.append(state)
  }

  var collectedCounter = 0
  for i in 0 ..< stack.count {
    stack[i].children.withUnsafeBufferPointer { ptr in
      let buffer = UnsafeMutableBufferPointer<Entry>.allocate(capacity: ptr.count)
      buffer.baseAddress!.initialize(from: ptr.baseAddress!, count: ptr.count)
      collectedCounter += ptr.count
      collected.append(buffer)
    }
    stack[i].children = []
  }

  let flatten = [Entry](unsafeUninitializedCapacity: collectedCounter) { (buffer: inout UnsafeMutableBufferPointer<Entry>, initialised: inout Int) in
    initialised = 0
    for pPtr in collected {
      buffer.baseAddress!.advanced(by: initialised).moveInitialize(from: pPtr.baseAddress!, count: pPtr.count)
      initialised += pPtr.count
      pPtr.deallocate()
    }

    precondition(initialised == collectedCounter)
  }

  print(flatten.count)
}


highLevel()
unsafe()