[Rd] Bug or feature: using "ANY" as a generic field class (was: '[R] Is there a (virtual) class that all R objects inherit from?)

[John Chambers]

Well, your mail is unclear as to what you expected, but there is one bug 
shown by your example.

The behavior of S4 classes is sensible, at least as far as the example 
shows:


 > setClass("A", representation(x="ANY"))
[1] "A"
 > setClass("B", contains="A", representation(x="character"))
[1] "B"
 > new("B", x=1:3)
Error in validObject(.Object) :
   invalid class "B" object: invalid object for slot "x" in class "B": 
got class "integer", should be or extend class "character"

You couldn't expect the new() call to work, as the error message clearly 
explains.  A legitimate call does work:

 > new("B", x = "abc")
An object of class "B"
Slot "x":
[1] "abc"

The reference classes should work the same way, but don't, as your 
example shows.

A <- setRefClass(
+ Class="A",
+ fields=list(
+ .PRIMARYDATA="ANY"
+ ),
+ contains=c("VIRTUAL")
+ )
 > B <- setRefClass(
+ Class="B",
+ fields=list(
+ .PRIMARYDATA="character"
+ ),
+ contains=c("A")
+ )
Error in `insertFields<-`(`*tmp*`, value = "character") :
   The overriding class("character") of field ".PRIMARYDATA" is not a 
subclass of the existing field definition ("ANY")

We'll fix that.  And, yes, "ANY" is intended as a universal superclass, 
but is usually not mentioned explicitly.


On 6/3/11 6:53 AM, Janko Thyson wrote:
> Dear list,
>
> I was wondering if you could help me out in clarifying something:
> Is it possible to use class "ANY" in slots/fields of formal classes if you
>     a) do not want to restrict valid classes of that field and
>     b) if you are making explicit use of class inheritance?
>
> It seems to work in simple scenarios but produces errors when class
> inheritance comes into play. So I was wondering if that's a feature or a
> bug.
>
> If using "ANY" is not the right way, I'd appreciate a pointer to how you
> can to this.
>
> See previous post with an example below.
>
> Regards,
> Janko
>
> On 06/03/2011 01:53 AM, Janko Thyson wrote:
>> On 31.05.2011 18:17, Martin Morgan wrote:
>>> On 05/30/2011 07:02 AM, Janko Thyson wrote:
>>>> Dear list,
>>>>
>>>> I would like to set one specific Reference Class field to be of an
>>>> arbitrary class. Is there a class that all R objects inherit from? I
>>>> thought that "ANY" was something like this, but obviously that's not
>>>> true:
>>>>
>>>>> inherits(1:3, "ANY")
>>>> [1] FALSE
>>>
>>> I can't speak to the implementation, but ANY functions as a base class
>>> in terms of slot / field assignment and inheritance, e.g.,
>>>
>>> setClass("A", representation(x="ANY"))
>>> new("A", x=1:3)
>>>
>>> Martin
>>
>> Hi Martin,
>>
>> sorry for the late response. The way you do it works. Yet, when you
>> declare dependencies more explicitly (contains=XY), then R complains. Is
>> this a feature or a bug (with respect to the "less explicit" way working
>> just fine)? See the example below:
>>
>> # S4
>> setClass("A", representation(x="ANY"))
>> new("A", x=1:3)
>>
>> setClass("A", representation(x="ANY"))
>> setClass("B", contains="A", representation(x="character"))
>> new("B", x=1:3)
>>
>> # Reference Classes
>> setRefClass(
>> Class="A",
>> fields=list(
>> .PRIMARYDATA="ANY"
>> ),
>> contains=c("VIRTUAL")
>> )
>> B<- setRefClass(
>> Class="B",
>> fields=list(
>> .PRIMARYDATA="character"
>> ),
>> contains=c("A")
>> )
>
> Bug, I'd say. Martin
>
>>
>> Regards,
>> Janko
>>>>
>>>> Regards,
>>>> Janko
>>>>
>>>> [[alternative HTML version deleted]]
>>>>
>>>> ______________________________________________
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>>>> https://stat.ethz.ch/mailman/listinfo/r-help
>>>> PLEASE do read the posting guide
>>>> http://www.R-project.org/posting-guide.html
>>>> and provide commented, minimal, self-contained, reproducible code.
>>>
>>>
>
>