[R] Calling any method within default method!

[Rui Barradas]

Hello,

Your foo.default is wrong in:

1) The general principle. S3 methods dispatch on the class attribute, 
you cannot expect to set that attribute in foo.default

  and have it call/dispatch
  and have it call/dispatch
  and ...

2) Even if this were possible, your assignment of the class attribute is 
wrong, you assign "foo.brazil" and "foo.argentina" so the methods to be 
called would be, respectively,

foo.foo.brazil
foo.foo.argentina

Nonsense! But in fact it's just a typo.

Try assigning just "brazil" or "argentina" and error 1) above (not very 
well explained, BTW) will still occur.


A possible solution is to have a different generic, bar(), with methods 
bar.brazil and bar.argentina. Something like this:


foo <- function (x, ...) UseMethod ('foo')

foo.default <- function(x, a = 10, b = NULL, cc = 2, dd = 3,
                         type = c('brazil', 'argentina'), ...){

   ty <- match.arg(type)

   obj <- list(a = a, b = b, cc = cc, dd = dd)
   class (obj) <- ty
   res <- bar(x = obj, ...)
   res
}

bar <- function (x, ...) UseMethod ('bar')
bar.brazil <- function(x, ...){
   a <- x$a
   cc <- x$cc
   res <- a + cc
   res
}

bar.argentina <- function(x, ...){
   cc <- x$cc
   dd <- x$dd
   res <- sqrt(cc + dd)
   res
}

foo(a = 1)
#[1] 3

foo(a = 1, type = 'argentina')
#[1] 2.236068


Hope this helps,

Rui Barradas


Às 00:34 de 29/05/19, Ivan Bezerra Allaman escreveu:
> Good night dear!
> For years I have a problem that I have avoided with the use of the switch
> function, but now I want to solve by following the good practices of object
> orientation (OOP).
> My function was created to generate experiments according to some input
> parameters. Therefore, the first argument does not have a class defined as
> "data.frame", "matrix", etc., so that from the generic, specific methods can
> be called.
> I made a simple example to show my problem.
> 
> foo <- function (x, ...) UseMethod ('foo')
> 
> foo.default <- function(x,
>                          a = 10,
>                          b = NULL,
>                          cc = 2,
>                          dd = 3,
>                          type = c ('brazil', 'argentina'),
>                          ...){
> 
>    ty <- match.arg(type)
> 
>    obj <- list(a = a,
>                   b = b,
>                   cc = cc,
>                   dd = dd)
>    class (obj) <- paste ('foo',
>                                     ty,
>                                    sep = '.')
> 
>    res <- foo(x = obj, ...)
> }
> 
> foo.brazil <- function(x, ...){
>    a <- x$a
>    cc <- x$cc
>    res <- a + cc
>    return (res)
> }
> 
> foo.argentina <- function(x, ...){
>    cc <- x$cc
>    dd <- x$dd
>    res <- sqrt(cc + dd)
>    return (res)
> }
> 
> foo(a = 1)
> 
> If anyone has any light I thank them immensely.
>