IterativeSelectGen.swift

public struct SelectGenerator<T> : GeneratorType {
  
  private let vals: [T]
  private var i: Int
  
  mutating public func next() -> (T, [T])? {
    guard ++i < vals.endIndex else { return nil }
    var ar = vals
    return (ar.removeAtIndex(i), ar)
  }
  
  public init(vals: [T]) {
    self.i = -1
    self.vals = vals
  }
}

var g = SelectGenerator(vals: [1, 2, 3, 4])

g.next() // (1, [2, 3, 4])
g.next() // (2, [1, 3, 4])
g.next() // (3, [1, 2, 4])
g.next() // (4, [1, 2, 3])
g.next() // nil