[R] S4 non-virtual class with no slots? [SOLVED]

Boylan, Ross Ross.Boylan at ucsf.edu
Sat Apr 23 02:33:15 CEST 2016

Thanks, Martin, that (inherit from a virtual class) worked great.  I already had a base class created with setUnion, and so this was an easy switch.

I had assumed that since inheriting from a class without slots would produce a class without slots the result would still be virtual.  Fortunately that's not the case.

From: Martin Morgan [martin.morgan at roswellpark.org]
Sent: Friday, April 22, 2016 2:36 PM
To: Boylan, Ross; r-help at r-project.org
Subject: Re: [R] S4 non-virtual class with no slots?

On 04/22/2016 04:38 PM, Boylan, Ross wrote:
> It seems that if an S4 class has no slots it can't be instantiated because it is assumed to be virtual.  Is there a way around this other than adding a do-nothing slot?  A singleton would be OK, though is not essential.
> Problem:
> EmptyFitResult <- setClass("EmptyFitResult", representation=representation())
> # also tried it without the second argument.  same result.
>   > e <- EmptyFitResult()
>   Error in new("EmptyFitResult", ...) :
>     trying to generate an object from a virtual class ("EmptyFitResult")
> This in R 3.1.1.
> Context:
> I fit simulated data; in some simulations none survive to the second stage of fitting.  So I just need a way to record that this happened, in a way that integrates with my other non-null results.

A not too artificial solution is to create a base class, with derived
classes corresponding to stateless or stateful conditions

Base = setClass("Base"); A = setClass("A", contains="Base"); A()

Martin Morgan

> Thanks.
> Ross Boylan
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