S4 class extends "data.frame", getDataPart sees "list"

R-Devel:

When I get the data part of an S4 class that contains="data.frame", it gives
me a list, even when the "data.frame" is the S4 version:

d<-data.frame(x=1:3)
isS4(d)

[1] FALSE                           # of course

dS4<-new("data.frame",d)
isS4(dS4)

[1] TRUE                            # ok

class(dS4)

[1] "data.frame"                   # good
attr(,"package")
[1] "methods"

setClass("A", representation(label="character"), contains="data.frame")

[1] "A"

a<-new("A",dS4, label="myFrame")
getDataPart(a)

[[1]]                                  # oh?
[1] 1 2 3

class(a at .Data)

[1] "list"                           # hmm

names(a)

[1] "x"                             # sure, that makes sense

a

Object of class "A"
   x
1 1
2 2
3 3
Slot "label":
[1] "myFrame"


Was I wrong to have expected the "data part" of 'a' to be a "data.frame"?

Thanks.

Dan Murphy

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