[R] Help with first S3-class

[Martin Møller Skarbiniks Pedersen]

On 3 January 2018 at 00:52, Duncan Murdoch <murdoch.duncan at gmail.com> wrote:
> On 02/01/2018 6:38 PM, Martin Møller Skarbiniks Pedersen wrote:
>>
>> Hi,
>>
>>    I am trying to understand S3 classes. I have read several tutorials
>> about
>> the topics but I am still a bit confused. I guess it is because it is
>> so different from
>> Java OOP.
>
>
> What you do below isn't S3.  S3 is a system where the classes are secondary
> to the generic functions.  Methods "belong" to generics, they don't belong
> to classes.  As far as I can see, you hardly make use of S3 methods and
> generics at all.

Here is my second attempt making a S3-class.
But something is wrong with the deposit.account() ? Thanks for any help.

I expect this output:

[1] 0
Martin
Saldo is:  100

but I get this:

[1] 100
Martin
Saldo is:  0

Regards
Martin

account <- function(owner = NULL) {
if (is.null(owner)) stop("Owner can't be NULL")
value <- list(owner = owner, saldo = 0)
attr(value, "class") <- "account"
value
}

balance <- function(obj) { UseMethod("balance") }

balance.account <- function(obj) {
obj$saldo
}

deposit <- function(obj, amount) { UseMethod("deposit") }

deposit.account <- function(obj, amount) {
obj$saldo <- obj$saldo + amount
}

print.account <- function(obj) {
cat(obj$owner, "\n")
cat("Saldo is: ", obj$saldo, "\n")
}

A1 <- account("Martin")
deposit(A1, 100)
balance(A1)
print(A1)