ArgRecords.swift

class ArgRecords<T>{
 private(set) var history: [T] = []
 func record(_ t: T){
  history.append(t)
 }
 subscript(_ i: Int) -> T? {
  guard i < history.count else {return nil}
  return history[i]
 }
 var count: Int {
  return history.count
 }
}