[R] Scope and assignment: baffling

[Gabor Grothendieck]

The code you presented is very close to object oriented in the style
of the proto package.  For example,

library(proto)

# generate a single object p
p <- proto(a = 0,
	geta = function(.) .$a,
	incra = function(.) .$a <- .$a + 5)

p$geta()
p$a # same
p$incra()
p$geta()


# Or if you want to be able to generate objects like that:

Account <- function() proto(a = 0,
	geta = function(.) .$a,
	incra = function(.) .$a <- .$a + 5)

# pp is an Account object
pp <- Account()
pp$geta()
pp$a # same
pp$incra()
pp$geta()

See http://r-proto.googlecode.com for more info.


On Wed, Mar 31, 2010 at 9:44 PM, Jeff Brown <dopethatwantscash at yahoo.com> 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?
>
> Thanks,
> Jeff
> --
> View this message in context: http://n4.nabble.com/Scope-and-assignment-baffling-tp1747582p1747582.html
> Sent from the R help mailing list archive at Nabble.com.
>
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