On Sat, Mar 19, 2011 at 8:02 PM, Russ Abbott <russ.abb...@gmail.com> wrote:
> Actually, I guess I'm not really talking about objects. I was looking
> through the scoping demo. It uses this function.
>
>> open.account <- function(total) {
>
> +
>
> + list(
>
> + deposit = function(amount) {
>
> + if(amount <= 0)
>
> + stop("Deposits must be positive!\n")
>
> + total <<- total + amount
>
> + cat(amount,"deposited. Your balance is", total, "\n\n")
>
> + },
>
> + withdraw = function(amount) {
>
> + if(amount > total)
>
> + stop("You don't have that much money!\n")
>
> + total <<- total - amount
>
> + cat(amount,"withdrawn. Your balance is", total, "\n\n")
>
> + },
>
> + balance = function() {
>
> + cat("Your balance is", total, "\n\n")
>
> + }
>
> + )
>
> + }
>
> I wanted to re-write the function so that instead of referring to total in
> deposit and withdraw I could refer to balance. Something like this,
>
> withdraw = function(amount) {
> + if(amount > total)
> + stop("You don't have that much money!\n")
> + total <<- total - amount
> + cat(amount,"withdrawn. Your balance is", this,balance(),
> "\n\n")
>
> But that doesn't work. Is it possible to do this?
> Thanks.
>
Try this:
open.account <- function(total) {
this <- environment()
list(...same list as before...)
}
Now within the body of any of the methods in the list, this$total
refers to the balance.
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