Jeff Brown wrote:
> Hi,
>
> The code below creates a value, x$a, which depending on how you access it
> evaluates to its initial value, or to what it's been changed to. The last
> two lines should, I would have thought, evaluate to the same value, but they
> don't.
>
> f <- function () {
> x <- NULL;
> x$a <- 0;
> x$get.a <- function () {
> x$a;
> };
> x$increment.a <- function () {
> x$a <<- x$a + 5;
> };
> x
> };
> x <- f();
> x$increment.a();
> x$get.a();
> x$a;
>
> This can be repeated; each time you call x$increment.a(), the value
> displayed by x$get.a() changes, but x$a continues to be zero.
>
> Is that totally weird, or what?
In a word, no. It's not the same x. (And R is not Java or C++). It
should be enlightening to try
evalq(x,environment(x$get.a))
--
Peter Dalgaard
Center for Statistics, Copenhagen Business School
Phone: (+45)38153501
Email: pd....@cbs.dk Priv: pda...@gmail.com
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