In addition to Duncan Murdoch's explanation, this is discussed in the
documentation for "Classes" (briefly):
.....
Extending a basic type this way allows objects to use old-style code for
the corresponding type as well as S4 methods. Any basic type can be used
for .Data, but a few types are treated differently because they do not
behave like ordinary objects; for example, "NULL", environments, and
external pointers. Classes extend these types by using a specially named
slot, itself inherited from an internally defined S4 class. Inheritance
from the nonstandard object type then requires an actual computation,
rather than the "simple" inclusion for other types and classes. The
intent is that programmers will not need to take account of the
mechanism, but one implication is that you should not explicitly use the
type of an S4 object that extends an arbitrary object type. Use is and
similar functions instead.
.......
The code for is.environment() is presumably using the type, whereas
inherits() takes account of the indirect mechanism.
Generally, you should be able to deal with inheritance from environments
in a natural way.
John
On 4/24/10 10:15 AM, Christopher Brown wrote:
I looked through the documentation and the mailing lists and could not
find an answer to this. My apologies if it has already been answered.
If it has, a pointer to the relevant discussion would be greatly
appreciated.
Creating S4 classes containing environments exhibits unexpected
behavior/features. These have a different in two ways:
1) slotName for the data: ".xData" instead of ".Data" and do not respond to the
2) Response to the is.* function seems to indicate that the object
does not know of its inheritance. ( Notably, the inherits function
works as expected. )
Here is a working illustration:
# LIST
setClass( 'inheritList', contains='list')
[1] "inheritList"
inList<- new( 'inheritList' )
class( inList )
[1] "inheritList"
attr(,"package")
[1] ".GlobalEnv"
is.list( inList ) # TRUE
[1] TRUE
slotNames(inList) # ".Data"
[1] ".Data"
inherits(inList, 'list' ) # TRUE
[1] TRUE
# ENVIRONMENT
setClass( 'inheritEnv', contains='environment' )
Defining type "environment" as a superclass via class ".environment"
[1] "inheritEnv"
inEnv<- new( 'inheritEnv' )
class(inEnv)
[1] "inheritEnv"
attr(,"package")
[1] ".GlobalEnv"
is.environment(inEnv) # FALSE
[1] FALSE
slotNames(inEnv) # ".xData"
[1] ".xData"
inherits(inEnv, 'environment' ) # TRUE
[1] TRUE
My questions is whether this behavior is a bug? By design? A work
around? Etc.?
Thanks kindly for your reply,
Chris
the Open Data Group
http://www.opendatagroup.com
http://blog.opendatagroup.com
______________________________________________
R-devel@r-project.org mailing list
https://stat.ethz.ch/mailman/listinfo/r-devel
______________________________________________
R-devel@r-project.org mailing list
https://stat.ethz.ch/mailman/listinfo/r-devel
