\Header{.Alias}{Create Alias (Pointer) to R Object}
\keyword{programming}{.Alias}
\begin{Description}\relax
\code{.Alias} creates an \bold{alias} to another (part of) an \R{}
object which is more (memory-) efficient than usual assignment.\end{Description}
\begin{Usage}
\begin{verbatim}
new <- .Alias(expr)
\end{verbatim}
\end{Usage}
\begin{Arguments}
\begin{ldescription}
\item[\code{expr}] an \R{} expression; typically a name.
\item[\code{new}] new name by which \code{expr} can be accessed.
\end{ldescription}
\end{Arguments}
\begin{Value}
\emph{an identical copy} of \code{expr}.\end{Value}
\begin{Section}{Warning}
This has a \bold{dangerous} semantic, and consequences can be
unexpected (it can be used to defeat the call-by-value illusion).
Know what you are doing \emph{before} using \code{.Alias}!\end{Section}
\begin{SeeAlso}\relax
\code{\Link{<\Rdash}} for usual assignments.\end{SeeAlso}
\begin{Examples}
\begin{ExampleCode}
mop <- options()
mop$browser <- "a browser"   # not set on all platforms
Op <- .Alias(mop)
## A change to mop is reflected in Op and vice versa
## -- ONLY if no new slots are created ...
mop$digits <- "Wow!"
Op$browser <- "another one"
mop$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: still the old one, i.e. NULL
all(names(mop) == names(Op))# no longer TRUE
\end{ExampleCode}
\end{Examples}

