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.
Ross
________________________________________
From: Martin Morgan [martin.mor...@roswellpark.org]
Sent: Friday, April 22, 2016 2:36 PM
To: Boylan, Ross; r-help@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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