R devel - Oct 2010 - Reference Classes: Generalizing Reference Class Generator objects?

Is it possible to override the $new(...) in the reference class 
generator? I have tried adding a "new" method to the methods of the 
class, but that is obviously not correct. I have also tried adding it to 
the class generator, but the class generator still uses the default 
constructor.

As a simple example, this is the current interface:
TestClass <- setRefClass ("TestClass",
         fields = list (text = "character"),
         methods = list (
                 print = function ()  {cat(text)})
)
test <- TestClass$new (text="Hello World")
test$print()

I would like to override $new(...) to be something like (add a "\n" to
the end of the input, no need to specify input fields):
TestClass$methods (new = function (text) {
             text <- paste (text, "\n")
             methods:::new (def, text=text)
         })

The constructor would then be:
test <- TestClass$new ("Hello World")

This is a subtle, but useful change. I have also tried adding to 
TestClass a method $newInstance(text), but that was not successful. If 
this is not possible, could we consider augmenting the Reference Class 
interface to include constructors?

Hi Daniel,

I think you want to define an "initialize" method, as in

TestClass <- setRefClass ("TestClass",
       fields = list (text = "character"),
       methods = list (
               initialize = function (text) { object <-
initFields(text=paste(text,"\n")) },
               print = function ()  { cat(text) } )
)

This seems to work as you intend:
> x <- TestClass$new("test")
> x$print()
test


All the best,
Jon

On 28 October 2010 15:13, Daniel Lee <bearlee at alum.mit.edu>
wrote:
> Is it possible to override the $new(...) in the reference class generator?
I
> have tried adding a "new" method to the methods of the class, but
that is
> obviously not correct. I have also tried adding it to the class generator,
> but the class generator still uses the default constructor.
>
> As a simple example, this is the current interface:
> TestClass <- setRefClass ("TestClass",
> ? ? ? ?fields = list (text = "character"),
> ? ? ? ?methods = list (
> ? ? ? ? ? ? ? ?print = function () ?{cat(text)})
> )
> test <- TestClass$new (text="Hello World")
> test$print()
>
> I would like to override $new(...) to be something like (add a
"\n" to the
> end of the input, no need to specify input fields):
> TestClass$methods (new = function (text) {
> ? ? ? ? ? ?text <- paste (text, "\n")
> ? ? ? ? ? ?methods:::new (def, text=text)
> ? ? ? ?})
>
> The constructor would then be:
> test <- TestClass$new ("Hello World")
>
> This is a subtle, but useful change. I have also tried adding to TestClass
a
> method $newInstance(text), but that was not successful. If this is not
> possible, could we consider augmenting the Reference Class interface to
> include constructors?
>
> ______________________________________________
> R-devel at r-project.org mailing list
> https://stat.ethz.ch/mailman/listinfo/r-devel
>

Sorry - you don't need to assign the value of initFields(). I was
going to do it in two lines but then realised one was enough... :)

TestClass <- setRefClass ("TestClass",
       fields = list (text = "character"),
       methods = list (
               initialize = function (text) {
initFields(text=paste(text,"\n")) },
               print = function ()  { cat(text) } )
)

All the best,
Jon


On 28 October 2010 15:13, Daniel Lee <bearlee at alum.mit.edu>
wrote:
> Is it possible to override the $new(...) in the reference class generator?
I
> have tried adding a "new" method to the methods of the class, but
that is
> obviously not correct. I have also tried adding it to the class generator,
> but the class generator still uses the default constructor.
>
> As a simple example, this is the current interface:
> TestClass <- setRefClass ("TestClass",
> ? ? ? ?fields = list (text = "character"),
> ? ? ? ?methods = list (
> ? ? ? ? ? ? ? ?print = function () ?{cat(text)})
> )
> test <- TestClass$new (text="Hello World")
> test$print()
>
> I would like to override $new(...) to be something like (add a
"\n" to the
> end of the input, no need to specify input fields):
> TestClass$methods (new = function (text) {
> ? ? ? ? ? ?text <- paste (text, "\n")
> ? ? ? ? ? ?methods:::new (def, text=text)
> ? ? ? ?})
>
> The constructor would then be:
> test <- TestClass$new ("Hello World")
>
> This is a subtle, but useful change. I have also tried adding to TestClass
a
> method $newInstance(text), but that was not successful. If this is not
> possible, could we consider augmenting the Reference Class interface to
> include constructors?
>
> ______________________________________________
> R-devel at r-project.org mailing list
> https://stat.ethz.ch/mailman/listinfo/r-devel
>