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

[Jeff Newmiller]

Isn't this why NULL is different than NA?

Alternatively,  what about using a data frame with no rows? 
-- 
Sent from my phone. Please excuse my brevity.

On April 22, 2016 1:38:57 PM PDT, "Boylan, Ross" <Ross.Boylan at ucsf.edu> 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.
>
>Thanks.
>Ross Boylan
>
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