In R-devel (svn 49628) and back to at least R 2.7.0 we get
inconsistent results when attempting to attach attributes to
a variable with the value NULL.
If we use attributes<- it finishes but changes the value to list().
> a<-NULL
> attributes(a)<-list(attr1="First attribute", attr2=2+2i)
> a
list()
attr(,"attr1")
[1] "First attribute"
attr(,"attr2")
[1] 2+2i
If we use attr<- it refuses to attach the attribute
> b<-NULL
> attr(b, "attr1") <- "First attribute"
Error in attr(b, "attr1") <- "First attribute" :
attempt to set an attribute on NULL
Is the second behavior the correct one and should attributes(x)<-list()
abort if x is NULL?
(attributes(NULL)<-list(attr="First") dies because NULL itself is not
allowed on the left side of an assignment.)
Bill Dunlap
TIBCO Software Inc - Spotfire Division
wdunlap tibco.com
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