[R] "registering" a generic method for a class

[Matthias Kohl]

In case of S4 objects "show" is called. Hence, you should implement new 
S4-methods for show ...

Matthias


m.u.r. wrote:
> Sorry in advance if this is too simple a question, but I'm stuck with
> some odd behavior and I can't find the text to rid myself of this
> (admittedly somewhat trivial) problem.  Note that I've done generic
> programming with S3 "objects" in the past, but I've never really
> dabbled in creating S4 objects until now.
>
> So, I've created a new S4 class, call it "myclass", e.g. :
>
>   
>> setClass("myclass", representation(slot1 = "list"));
>>     
>
> And I've also created an implementation of "print" for this class via:
>
>   
>> setMethod("print", "myclass", function(x) { print(paste("a myclass instance with a list of length", length(x at slot1), "in slot1")); });
>>     
>
> Now I can create a new object, say via:
>
>   
>> myobj <- new("myclass", slot1 = list());
>>     
>
> The question now is the difference in output when I type the object
> name alone on the command prompt vs when I type print(myobj) on the
> command prompt, as seen below:
>
>   
>> myobj
>>     
> An object of class “myclass”
> Slot "slot1":
> list()
>
>   
>> print(myobj)
>>     
> [1] "a myclass instance with a list of length 0 in slot1"
>
> I thought that the "print" method is called when an object is called
> from the command line, and to check this I checked the registered
> implementations of "print" via:
>
>   
>> methods("print")
>>     
>
> and in the long output I didn't see the "print.myclass" version.  I
> had thought that the setMethod method would essentially create this
> function for me... but I must be missing a key step somewhere along
> the line.  Can anyone help me figure out what I would need to do to
> get the generic version of the method (in this toy example, "print")
> to see my class' method as an implementation of the generic?  Thanks
> much for any help!
>
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>   

-- 
Dr. Matthias Kohl
www.stamats.de