R help - Jun 2009 - S4: Initialization method called during setClass??

Dear UseRs,

A simple class inheritance example:
> setClass("test",representation(a="numeric"))
> setMethod("initialize","test",
           function(.Object,x,...){
               print("Initialization!!!")
               callNextMethod(.Object,a=x,...)
           })
> new("test",x=23)
[1] "Initialization!!!"
An object of class "test"
Slot "a":
[1] 23
>
setClass("test2",contains="test",representation(b="integer"))
[1] "Initialization!!!"
Error in .nextMethod(.Object, a = x, ...) : 
  argument "x" is missing, with no default


When trying to define a new class "test2" above,
"initialize" method for "test" is called (??? looks like a
bug to me) and naturally argument "x" is not found. Thus I can not
create a subclass for "test".

I could not find anything in documentation. 

Thanks,
Vitalie.

Hi Vitalie --

Vitalie S. wrote:
> Dear UseRs,
> 
> A simple class inheritance example:
> 
>> setClass("test",representation(a="numeric"))
>> setMethod("initialize","test",
>           function(.Object,x,...){
>               print("Initialization!!!")
>               callNextMethod(.Object,a=x,...)
>           })
> 
>> new("test",x=23)
> [1] "Initialization!!!"
> An object of class "test"
> Slot "a":
> [1] 23
the implicit contract is that the initialize method is written so that
new("test") works. This contract comes up at several points during
class
definition and instantiation. You've identified one of those points.
> 
>>
setClass("test2",contains="test",representation(b="integer"))
> [1] "Initialization!!!"
> Error in .nextMethod(.Object, a = x, ...) : argument "x" is
missing,
> with no default
I'm not sure of the details, but part of the class definition is a
coercion method, and in defining this new() is called, without
arguments, on the contained classes.

Martin
> 
> 
> When trying to define a new class "test2" above,
"initialize" method for
> "test" is called (??? looks like a bug to me) and naturally
argument "x"
> is not found. Thus I can not create a subclass for "test".
> I could not find anything in documentation.
> Thanks,
> Vitalie.
> 
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