[<-.POSIXlt changes order of attributes (PR#9197)

Hello,

Prof Brian Ripley wrote:

Please point us to the documentation that says attributes are ordered.
E.g. R-lang.texi says

  All objects except @code{NULL} can have one or more attributes attached
  to them.  Attributes are stored as a list where all elements are named.

(although in fact they are stored in a pairlist).

I know of tens of functions that change the order of attributes, and 
did look at teaching identical() that they are not ordered.  But 
since they are stored as a pairlist, it would be quite expensive.

I agree that there is no need for attributes to be always in the same
order as this is tedious to achieve as you noted above, but identical()
seems to care about this.

(Given that attributes seem to be growing in use, another internal storage 
mechanism is becoming more appropriate.)

Which internal storage mechanism are you talking about here?