Hi.
On Fri, Aug 26, 2011 at 8:58 AM, Ben qant <ccqu...@gmail.com> wrote:
> If someone is able, can you tell me if there is a better way to do this?
> More specifically, do I have to rewrite all of the data members stuff and
> extend stuff of parent class in the child class?
No.
> See below. Thanks in
> advance!
>
> Example 1:
>
> setConstructorS3("ClassA", function(A,x) {
> if(missing(A))A=15;
> if(missing(x))x=NA;
> extend(Object(), "ClassA",
> .size = A,
> .x=x
> )
> })
> setMethodS3("getSize", "ClassA", function(this,...) {
> this$.size;
> })
> setMethodS3("getX", "ClassA", function(this,...) {
> this$.x;
> })
>
> setConstructorS3("ClassB", function(A,x,bData) {
> if(missing(bData))bData = NA;
> extend(ClassA(), "ClassB",
> .bData = bData
> )
> })
The key is to understand that that inner ClassA() is a just regular
function call that returns an object of class "ClassA" [with full
class attribute vector c("ClassA", "Object")]. Since it is a regular
function you can pass arguments to it as well, so in your case just
do:
setConstructorS3("ClassB", function(A,x,bData) {
if(missing(A))A=15;
if(missing(x))x=NA;
if(missing(bData))bData = NA;
extend(ClassA(A=A, x=x), "ClassB",
.bData = bData
)
})
or more generic:
setConstructorS3("ClassB", function(..., bData) {
if(missing(bData)) bData = NA;
extend(ClassA(...), "ClassB",
.bData = bData
)
})
Personally, I also try to avoid using missing() and instead using
default argument values, i.e.
setConstructorS3("ClassA", function(A=15, x=NA) {
extend(Object(), "ClassA",
.size = A,
.x=x
)
})
setConstructorS3("ClassB", function(..., bData=NA) {
extend(ClassA(...), "ClassB",
.bData = bData
)
})
which also makes things cleaner.
Hope this helps
/Henrik
(author of R.oo)
> setMethodS3("getBData", "ClassB", function(this,...) {
> this$.bData;
> })
>
> Usage:
>> b = ClassB(13,100,6)
>> b$getSize() # I expected to get 13.
> [1] 15
>> b$getBData()
> [1] 6
>> b$getX()
> [1] NA # Same thing here. I expected 100.
>
>
> I corrected it by rewriting the ClassA data member defaults and the ClassA
> extend() stuff within the ClassB class.
>
> Example 2:
>
> setConstructorS3("ClassA", function(A,x) {
> if(missing(A))A=15;
> if(missing(x))x=NA;
> extend(Object(), "ClassA",
> .size = A,
> .x=x
> )
> })
> setMethodS3("getSize", "ClassA", function(this,...) {
> this$.size;
> })
> setMethodS3("getX", "ClassA", function(this,...) {
> this$.x;
> })
>
> setConstructorS3("ClassB", function(A,x,bData) {
> if(missing(bData))bData = NA;
> if(missing(A))A=15; #added
> if(missing(x))x=NA; #added
> extend(ClassA(), "ClassB",
> .bData = bData,
> .x=x, #added
> .size=A #added
> )
> })
> setMethodS3("getBData", "ClassB", function(this,...) {
> this$.bData;
> })
>
>> b = ClassB(13,100,6)
>> b$getSize()
> [1] 13
>> b$getBData()
> [1] 6
>> b$getX()
> [1] 100
>
> Thanks for your help!
>
> Ben
>
> [[alternative HTML version deleted]]
>
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