[R] How to reduce key strokes when defining S4 classes?

[Peng Yu]

On Mon, Oct 26, 2009 at 11:56 PM,  <mtmorgan at fhcrc.org> wrote:
> Quoting Peng Yu <pengyu.ut at gmail.com>:
>
>> I feel tedious when I define a S4 class and the methods. For each
>> method, I have to call both setMethod and setGeneric (or both
>> setReplaceMethod and setGeneric). I would like a more compact grammar
>> so that I can reduce the key strokes. I'm wondering if there is a
>> better way available.
>>
>> setClass(
>>    Class='A',
>>    representation=representation(
>>        x='numeric'
>>        )
>>    )
>>
>> setMethod(
>>    f='initialize',
>>    signature='A',
>>    definition=function(.Object,x){
>>      cat("~~~ A: initializator ~~~\n")
>>      .Object<-callNextMethod(.Object,x=x)
>>      return(.Object)
>>    }
>>    )
>>
>> setGeneric('getx', function(object){
>>      standardGeneric('getx')
>>    }
>>    )
>>
>> setMethod('getx', 'A',
>>    function(object){
>>      return(object at x)
>>    }
>>    )
>
> in some sense getx is redundant; x(obj) can only extract a value; more so
> with setx(obj) <- value and x(obj) <- value (illustrating partly that 'x' is
> a poor name for a slot).
>
>>
>> setGeneric('setx<-', function(.object,value){
>>      standardGeneric('setx<-')
>>    }
>>    )
>>
>> setReplaceMethod(f='setx', signature='A',
>>    def=function(.object,value){
>>      .object at x<-value
>>      return(.object)
>>    }
>>    )
>
> one can create ad hoc getter / setter writers (e.g., in the Bioconductor
> GSEABase package), but in the long run I have found these to require more
> thought than the saved keystrokes are worth. You might be more clever /
> disciplined than I. It's tempting to write getters / setters as simple
> functions (setGeneric / setMethod is required because the defined 'generic'
> isn't really that generic, it's just an idiosyncratic accessor)  but in the
> long run this also doesn't seem to work well.

I just gave some examples on getters and setters. But I didn't only
mean getters and setters. Other methods also need the associated two
functions (setGeneric and setMethod) for their definition. I'd wish
there is a more cleaner way to define a method. One drawback of the
current way is the redundancy in the code. For example, 'getx' appears
twice (in both setGeneric and setMethod). This redundancy causes a
higher maintenance cost than if there were no such redundancy.

>> a=new(Class='A',x=10)
>> print(getx(a))
>>
>> setx(a)<-5
>> print(getx(a))
>>
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>
>
>
>