[Rd] S4 slot with NA default

[Peter Dalgaard]

Robin Hankin wrote:
> Hi
>
> How do I specify an S4 class with a slot that is potentially numeric,  
> but NA
> by default?  I   want the slot to be NA until I calculate its value
>   (an expensive operation, not needed for all applications).   When  
> its value is
> known, I  will create a new object with the correct value inserted in  
> the slot.
>
> I want "NA" to signify "not known".
>
> My attempt fails because NA is not numeric:
>
>  >  
> setClass 
> ("foo",representation=representation(x="numeric"),prototype=list(x=NA))
> Error in makePrototypeFromClassDef(properties, ClassDef, immediate,  
> where) :
>    in making the prototype for class "foo" elements of the prototype  
> failed to match the corresponding slot class: x (class “numeric” )
>  >
>
> (the real application has other slots too).   I can
> use "NaN", which is numeric:
>
>  >  
> setClass 
> ("foo",representation=representation(x="numeric"),prototype=list(x=NaN))
> [1] "foo"
>  >
>
> But this is not the correct sense: to me "NaN" means "not a number"  
> and I want
> the sense to be "not available".
>
>
>
> Any advice?
>
>
>
>   
How about NA_real_ or NA_integer_?


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