[R] Validity check when setting slot

[Vitalie S.]

Hi,

>>
>>     RG> Hi,
>>     RG> I'm wondering if the following behaviour is normal:
>>
>>     RG> setClass('A', representation(number='numeric'),     RG>  
>> validity=function(object){     RG> if( object at number < -1 )  
>> return("Invalid number"); TRUE})
>>     >> [1] "A"
>>     RG> a <- new('A')
>>     RG> a
>>     >> An object of class “A”
>>     >> Slot "number":
>>     >> numeric(0)
>>
>>     RG> a at number <- 0
>>     RG> a at number <- -3
>>     RG> a
>>     >> An object of class “A”
>>     >> Slot "number":
>>     >> [1] -3
>>

Rewriting `@<-` will do the job:

setClass('A', representation(number='numeric'),
           validity=function(object){
                         if( object at number < -1 ) return("Invalid number")
                         TRUE}
)


setMethod("@<-",
     signature(object = "A"),
     function (object, name, value){
         object <- callNextMethod(object, as.character(substitute(name)),  
value)
         validObject(object)
         return(object)
     }
)


> a <- new('A')
> a at number <- 23
> a at number <- -23
Error in validObject(object) : invalid class "A" object: Invalid number


By th way, it seems (to me) that there is a bug in callNextMethod above:

         object <- callNextMethod(object, name, value)
or
         object <- callNextMethod()

trigger an error:

Error in checkSlotAssignment(object, name, value) :
   "name" is not a slot in class "A"

-Vitalie