

   CCrreeaattee ````AAlliiaass'''' ((PPooiinntteerr)) ttoo OObbjjeecctt

        new <- .Alias(expr)

   AArrgguummeennttss::

       expr: an R expression; typically a name.

        new: new name by which `expr' can be accessed.

   DDeessccrriippttiioonn::

        `.Alias' creates an alias to another (part of) an R
        object which is more (memory-) efficient than usual
        assignment.

   VVaalluuee::

        an identical copy of `expr'.

   WWAARRNNIINNGG::

        This has a dangerous semantic, and consequences can be
        unexpected (it can be used to defeat the call-by-value
        illusion).  Know what you are doing before using
        `.Alias'!

   SSeeee AAllssoo::

        `<-' for usual assignments.

   EExxaammpplleess::

        mop <- options()
        Op <- .Alias(mop)
        ## A change to mop is reflected in Op and vice versa
        ## -- ONLY if no new slots are created ...
        mop $ digits <- "Wow!"
        Op  $ browser <- "Web broser"
        mop $ browser; Op $ digits
        all(names(mop) == names(Op) &
            sapply(seq(mop), function(i) all(Op[[i]] == mop[[i]])))
        ##> TRUE -- Op and mop  *ARE* the same thing !

        mop $ newslot <- pi #--->> 'newslot' ==> (shallow) COPY of 'mop'
         Op $ newslot# R (>= 0.63): still the old one, i.e. NULL
        all(names(mop) == names(Op))# no longer TRUE [R >= 0.63]

