From sfalcon at fhcrc.org  Tue Jan  3 16:53:00 2006
From: sfalcon at fhcrc.org (Seth Falcon)
Date: Tue, 03 Jan 2006 07:53:00 -0800
Subject: [Rd] S4 default initialization: unwanted NULL
Message-ID: <m2bqytfgv7.fsf@ziti.local>

The default initialization for slots of class "factor" and
"data.frame" gives NULL.  This seems odd, since those slots can't ever
be set to NULL by the user.  I would expect zero-length instances of
factor and data.frame.

Here is an example:

setClass("FOO", representation(a="factor", b="data.frame", c="numeric"))
[1] "FOO"
> ff <- new("FOO")
> ff
An object of class "FOO"
Slot "a":
NULL

Slot "b":
NULL

Slot "c":
numeric(0)


sessionInfo()
R version 2.3.0, 2005-12-26, powerpc-apple-darwin8.3.0 

attached base packages:
[1] "tools"     "methods"   "stats"     "graphics"  "grDevices" "utils"    
[7] "datasets"  "base"     


Slot c is initialized as I was expecting.

+ seth



[Rd] S4 default initialization: unwanted NULL
Seth Falcon