Simple class with an automatic printing issue

It may have to do with the results of is.object():

?> is.object(1*structure(1,class="testClass"))
?[1] FALSE
?> is.object(structure(1,class="testClass")*1)
?[1] TRUE
?> is.object(structure(1,class="testClass"))
?[1] TRUE

is.object(x) should be true if x has a class attribute,
but 1*structute(1,class="testClass") makes a thing
with a class attribute but without the 'OBJECT' bit set.

Bill Dunlap
TIBCO Software Inc - Spotfire Division
wdunlap tibco.com

-----Original Message-----
From: r-devel-bounces at r-project.org
[mailto:r-devel-bounces at r-project.org] On Behalf Of Tom Short
Sent: Sunday, April 12, 2009 4:00 PM
To: r-devel at r-project.org
Subject: [Rd] Simple class with an automatic printing issue

I don't understand the following behavior for a simple S3 class. The
auto-printing at the command line
doesn't behave as I expect. I'm probably missing something,
but it might be
a bug.

print.testClass <- function(x, ...) cat("Class:", class(x),

":", x, "\n")

structure(1, class = "testClass")

Class: testClass : 1

print(1 * structure(1, class = "testClass"))

Class: testClass : 1

1 * structure(1, class = "testClass") # why doesn't

auto-printing call
print.testClass here?
[1] 1
attr(,"class")
[1] "testClass"

structure(1, class = "testClass") * 1

Class: testClass : 1


platform ? ? ? i386-pc-mingw32
arch ? ? ? ? ? i386
os ? ? ? ? ? ? mingw32
system ? ? ? ? i386, mingw32
status ? ? ? ? RC
major ? ? ? ? ?2
minor ? ? ? ? ?9.0
year ? ? ? ? ? 2009
month ? ? ? ? ?04
day ? ? ? ? ? ?10
svn rev ? ? ? ?48318
language ? ? ? R
version.string R version 2.9.0 RC (2009-04-10 r48318)

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