At initialisation
     Contents are 1 2
In assignTo - assign to @_
     Contents now 1 2
In assignToRef - assign to ref. to @_
     Contents now 1 2
In listArgs - list of lexicals
     Contents now 1 2
In loopOver - loop over @_
     Contents now 2 3
In mapOver - increment @_ in map
     Contents now 3 4
In refToArray - take reference to @_ array
     Contents now 4 5
In refToElems - take reference to @_ elements
     Contents now 5 6
In shiftArgs - lexicals via shift
     Contents now 5 6
In useDirect - increment elements directly
     Contents now 6 7