[Rd] Unexpected failure when calling new() with unnamed arg and
Hi,
The man page for new() suggests that if 'a' is an object with slots
"slot1" and "slot2" and C is a class that extends the class of 'a',
then the 2 following calls should be equivalent:
new("C", a, ...)
new("C", slot1=a@slot1, slot2=a@slot2, ...)
This is generally the case but I just ran into a situation where it's
not. In the following example the former fails while the latter works:
setClass("A", representation(slot1="numeric", slot2="logical"))
setClass("B", contains="A", representation(design="formula"))
setClass("C", contains="B")
a <- new("A", slot1=77, slot2=TRUE)
new("C", a, design=x ~ y) # fails
new("C", slot1=a@slot1, slot2=a@slot2, design=x ~ y) # works
Note that new("B", a, design=x ~ y) works so the 3-level class
hierarchy is really needed in order to reproduce.
Probably related to this, I also noted that new("B") and/or new("C")
return invalid objects:
c <- new("C")
validObject(c)
# Error in validObject(c) :
# invalid class “C” object: invalid object for slot "design"
# in class "C": got class "S4", should be or extend class "formula"
is(c@design, "formula")
# [1] FALSE
class(c@design)
# [1] "S4"
Note that 'c' can be fixed:
c@design <- formula(NULL)
validObject(c)
# [1] TRUE
Maybe something that the default "initialize" method should take care
of?
Another singularity that is maybe at the root of all of this is that
the "formula" S4 class is virtual:
showClass("formula")
# Virtual Class "formula" [package "methods"]
#
# Slots:
#
# Name: .S3Class
# Class: character
#
# Extends: "oldClass"
so a bare call to new("formula") fails:
new("formula")
# Error in new("formula") :
# trying to generate an object from a virtual class ("formula")
Shouldn't new("formula") just return an "empty" S3 formula (like
formula(NULL) does), in the same way that new("integer") returns
an empty ordinary integer vector?
Thanks,
H.
> sessionInfo()
R version 3.2.0 Patched (2015-04-17 r68202)
Platform: x86_64-unknown-linux-gnu (64-bit)
Running under: Ubuntu 14.04.2 LTS
locale:
[1] LC_CTYPE=en_US.UTF-8 LC_NUMERIC=C
[3] LC_TIME=en_US.UTF-8LC_COLLATE=en_US.UTF-8
[5] LC_MONETARY=en_US.UTF-8LC_MESSAGES=en_US.UTF-8
[7] LC_PAPER=en_US.UTF-8 LC_NAME=C
[9] LC_ADDRESS=C LC_TELEPHONE=C
[11] LC_MEASUREMENT=en_US.UTF-8 LC_IDENTIFICATION=C
attached base packages:
[1] stats graphics grDevices utils datasets methods base
--
Hervé Pagès
Program in Computational Biology
Division of Public Health Sciences
Fred Hutchinson Cancer Research Center
1100 Fairview Ave. N, M1-B514
P.O. Box 19024
Seattle, WA 98109-1024
E-mail: hpa...@fredhutch.org
Phone: (206) 667-5791
Fax:(206) 667-1319
__
R-devel@r-project.org mailing list
https://stat.ethz.ch/mailman/listinfo/r-devel
Re: [Rd] Unexpected failure when calling new() with unnamed arg and
> Hervé Pagès
> on Tue, 12 May 2015 15:18:42 -0700 writes:
> Hi,
> The man page for new() suggests that if 'a' is an object with slots
> "slot1" and "slot2" and C is a class that extends the class of 'a',
> then the 2 following calls should be equivalent:
>new("C", a, ...)
>new("C", slot1=a@slot1, slot2=a@slot2, ...)
> This is generally the case but I just ran into a situation where it's
> not. In the following example the former fails while the latter works:
>setClass("A", representation(slot1="numeric", slot2="logical"))
>setClass("B", contains="A", representation(design="formula"))
>setClass("C", contains="B")
>a <- new("A", slot1=77, slot2=TRUE)
>new("C", a, design=x ~ y) # fails
>new("C", slot1=a@slot1, slot2=a@slot2, design=x ~ y) # works
> Note that new("B", a, design=x ~ y) works so the 3-level class
> hierarchy is really needed in order to reproduce.
> Probably related to this, I also noted that new("B") and/or new("C")
> return invalid objects:
>c <- new("C")
>validObject(c)
># Error in validObject(c) :
># invalid class “C” object: invalid object for slot "design"
># in class "C": got class "S4", should be or extend class "formula"
>is(c@design, "formula")
># [1] FALSE
>class(c@design)
># [1] "S4"
> Note that 'c' can be fixed:
>c@design <- formula(NULL)
>validObject(c)
># [1] TRUE
> Maybe something that the default "initialize" method should take care
> of?
> Another singularity that is maybe at the root of all of this is that
> the "formula" S4 class is virtual:
>showClass("formula")
># Virtual Class "formula" [package "methods"]
>#
># Slots:
>#
># Name: .S3Class
># Class: character
>#
># Extends: "oldClass"
> so a bare call to new("formula") fails:
>new("formula")
># Error in new("formula") :
># trying to generate an object from a virtual class ("formula")
> Shouldn't new("formula") just return an "empty" S3 formula (like
> formula(NULL) does), in the same way that new("integer") returns
> an empty ordinary integer vector?
Interesting .. and at least worth following.
One problem and historical reason for the current setup seems
that the "formula" S3 class is not from 'base' but 'stats' :
R's source, src/library/methods/R/BasicClasses.R,
lines 524 ff has the following comment block
| .OldClassesPrototypes is a list of S3 classes for which prototype
| objects are known & reasonable. The classes will reappear in
| .OldClassesList, but will have been initialized first in
| .InitBasicClasses. NB: the methods package will NOT set up
| prototypes for S3 classes except those in package base and for "ts"
| (and would rather not do those either). The package that owns the
| S3 class should have code to call setOldClass in its
| initialization.
So, when John Chambers wrote this, he envisioned that the
'stats' package would do "the correct thing" for its own classes.
OTOH, as history went, the stats package was never allowed to
depend on methods.
There are many other S3 classes from 'stats' which also end up
similarly, being defined via setOldClass() and that itself
produces a VIRTUAL class.
Also, another part of the (R source) comment above is no longer
quite accurate, e.g., "data.frame" is in .OldClassesPrototypes
but not in .OldClassesList ...
As I do agree that "formula" is much more basic than these other classes,
I'm currently looking at tweaks to the methods (and stats) code,
to get this to work as indeed - you mentioned above - we
already allow "empty S3 formula" objects anyway.
... half an hour later : Indeed, I've been able to use the above information
such that new("formula") and new("formula", y ~ x)
work.
However, your code above now --- with my changes --- would fail :
> setClass("A", representation(slot1="numeric", slot2="logical"))
> setClass("B", contains="A", representation(design="formula"))
> setClass("C", contains="B")
Error in reconcilePropertiesAndPrototype(name, slots, prototype, superClasses,
:
"B" is not eligible to be the data part of another class (must be a basic
class or a virtual class with no slots)
>
So, I am not yet committing my changes to R-devel.
Hopefully more on this, later today.
Martin Maechler,
ETH Zurich
> Thanks,
> H.
> > sessionInfo()
> R version 3.2.0 Patched (2015-04-17 r68202)
> Platform: x86_64-unknown-linux-gnu (64-bit)
> Running under: Ubuntu 14.04.2 LTS
> --
> Hervé Pagès
> Fred Hutchinson Cancer Research Center
[..]
__
R-devel@r-project.org mailing list
https://stat.ethz.ch/mailman/listinfo/r-devel
Re: [Rd] Unexpected failure when calling new() with unnamed arg and
Thanks Martin for looking into this. H.
On 05/13/2015 03:57 AM, Martin Maechler wrote:
Hervé Pagès
on Tue, 12 May 2015 15:18:42 -0700 writes:
Hi,
The man page for new() suggests that if 'a' is an object with slots
"slot1" and "slot2" and C is a class that extends the class of 'a',
then the 2 following calls should be equivalent:
new("C", a, ...)
new("C", slot1=a@slot1, slot2=a@slot2, ...)
This is generally the case but I just ran into a situation where it's
not. In the following example the former fails while the latter works:
setClass("A", representation(slot1="numeric", slot2="logical"))
setClass("B", contains="A", representation(design="formula"))
setClass("C", contains="B")
a <- new("A", slot1=77, slot2=TRUE)
new("C", a, design=x ~ y) # fails
new("C", slot1=a@slot1, slot2=a@slot2, design=x ~ y) # works
Note that new("B", a, design=x ~ y) works so the 3-level class
hierarchy is really needed in order to reproduce.
Probably related to this, I also noted that new("B") and/or new("C")
return invalid objects:
c <- new("C")
validObject(c)
# Error in validObject(c) :
# invalid class “C” object: invalid object for slot "design"
# in class "C": got class "S4", should be or extend class "formula"
is(c@design, "formula")
# [1] FALSE
class(c@design)
# [1] "S4"
Note that 'c' can be fixed:
c@design <- formula(NULL)
validObject(c)
# [1] TRUE
Maybe something that the default "initialize" method should take care
of?
Another singularity that is maybe at the root of all of this is that
the "formula" S4 class is virtual:
showClass("formula")
# Virtual Class "formula" [package "methods"]
#
# Slots:
#
# Name: .S3Class
# Class: character
#
# Extends: "oldClass"
so a bare call to new("formula") fails:
new("formula")
# Error in new("formula") :
# trying to generate an object from a virtual class ("formula")
Shouldn't new("formula") just return an "empty" S3 formula (like
formula(NULL) does), in the same way that new("integer") returns
an empty ordinary integer vector?
Interesting .. and at least worth following.
One problem and historical reason for the current setup seems
that the "formula" S3 class is not from 'base' but 'stats' :
R's source, src/library/methods/R/BasicClasses.R,
lines 524 ff has the following comment block
| .OldClassesPrototypes is a list of S3 classes for which prototype
| objects are known & reasonable. The classes will reappear in
| .OldClassesList, but will have been initialized first in
| .InitBasicClasses. NB: the methods package will NOT set up
| prototypes for S3 classes except those in package base and for "ts"
| (and would rather not do those either). The package that owns the
| S3 class should have code to call setOldClass in its
| initialization.
So, when John Chambers wrote this, he envisioned that the
'stats' package would do "the correct thing" for its own classes.
OTOH, as history went, the stats package was never allowed to
depend on methods.
There are many other S3 classes from 'stats' which also end up
similarly, being defined via setOldClass() and that itself
produces a VIRTUAL class.
Also, another part of the (R source) comment above is no longer
quite accurate, e.g., "data.frame" is in .OldClassesPrototypes
but not in .OldClassesList ...
As I do agree that "formula" is much more basic than these other classes,
I'm currently looking at tweaks to the methods (and stats) code,
to get this to work as indeed - you mentioned above - we
already allow "empty S3 formula" objects anyway.
... half an hour later : Indeed, I've been able to use the above information
such that new("formula") and new("formula", y ~ x)
work.
However, your code above now --- with my changes --- would fail :
> setClass("A", representation(slot1="numeric", slot2="logical"))
> setClass("B", contains="A", representation(design="formula"))
> setClass("C", contains="B")
Error in reconcilePropertiesAndPrototype(name, slots, prototype,
superClasses, :
"B" is not eligible to be the data part of another class (must be a basic
class or a virtual class with no slots)
>
So, I am not yet committing my changes to R-devel.
Hopefully more on this, later today.
Martin Maechler,
ETH Zurich
Thanks,
H.
> sessionInfo()
R version 3.2.0 Patched (2015-04-17 r68202)
Platform: x86_64-unknown-linux-gnu (64-bit)
Running under: Ubuntu 14.04.2 LTS
--
Hervé Pagès
Fred Hutchinson Cancer Research Center
[..]
--
Hervé Pagès
Program in Computational Biology
Division of Public Health Sciences
Fred Hutchinson Cancer Research Center
1100 Fairview Ave. N, M1-B514
P.O. Box 19024
Seattle, WA 98109-1024
E-mail: hpa...@fredhutch.org
Phone: (206) 667-5791
Fax:(206) 667-1319
__
R-devel@r-project.org mailing list
https://stat
Re: [Rd] Unexpected failure when calling new() with unnamed arg and
Hi,
I realize this is an old thread, but just wondering whether a conclusion
was ever reached on this issue? I'm using formula(NULL) but it would be
nice if default initialization worked for formula classes as well.
Cheers,
Josh
On Thu, May 14, 2015 at 8:13 AM, Hervé Pagès wrote:
> Thanks Martin for looking into this. H.
>
>
> On 05/13/2015 03:57 AM, Martin Maechler wrote:
>
>> Hervé Pagès
>>> on Tue, 12 May 2015 15:18:42 -0700 writes:
>>>
>>
>> Hi,
>>>
>>
>> The man page for new() suggests that if 'a' is an object with slots
>>> "slot1" and "slot2" and C is a class that extends the class of 'a',
>>> then the 2 following calls should be equivalent:
>>>
>>
>> new("C", a, ...)
>>> new("C", slot1=a@slot1, slot2=a@slot2, ...)
>>>
>>
>> This is generally the case but I just ran into a situation where it's
>>> not. In the following example the former fails while the latter works:
>>>
>>
>> setClass("A", representation(slot1="numeric", slot2="logical"))
>>> setClass("B", contains="A", representation(design="formula"))
>>> setClass("C", contains="B")
>>> a <- new("A", slot1=77, slot2=TRUE)
>>>
>>
>> new("C", a, design=x ~ y) # fails
>>> new("C", slot1=a@slot1, slot2=a@slot2, design=x ~ y) # works
>>>
>>
>> Note that new("B", a, design=x ~ y) works so the 3-level class
>>> hierarchy is really needed in order to reproduce.
>>>
>>
>> Probably related to this, I also noted that new("B") and/or new("C")
>>> return invalid objects:
>>>
>>
>> c <- new("C")
>>>
>>
>> validObject(c)
>>> # Error in validObject(c) :
>>> # invalid class “C” object: invalid object for slot "design"
>>> # in class "C": got class "S4", should be or extend class "formula"
>>>
>>
>> is(c@design, "formula")
>>> # [1] FALSE
>>>
>>
>> class(c@design)
>>> # [1] "S4"
>>>
>>
>> Note that 'c' can be fixed:
>>>
>>
>> c@design <- formula(NULL)
>>>
>>
>> validObject(c)
>>> # [1] TRUE
>>>
>>
>> Maybe something that the default "initialize" method should take care
>>> of?
>>>
>>
>> Another singularity that is maybe at the root of all of this is that
>>> the "formula" S4 class is virtual:
>>>
>>
>> showClass("formula")
>>> # Virtual Class "formula" [package "methods"]
>>> #
>>> # Slots:
>>> #
>>> # Name: .S3Class
>>> # Class: character
>>> #
>>> # Extends: "oldClass"
>>>
>>
>> so a bare call to new("formula") fails:
>>>
>>
>> new("formula")
>>> # Error in new("formula") :
>>> # trying to generate an object from a virtual class ("formula")
>>>
>>
>> Shouldn't new("formula") just return an "empty" S3 formula (like
>>> formula(NULL) does), in the same way that new("integer") returns
>>> an empty ordinary integer vector?
>>>
>>
>> Interesting .. and at least worth following.
>>
>> One problem and historical reason for the current setup seems
>> that the "formula" S3 class is not from 'base' but 'stats' :
>>
>> R's source, src/library/methods/R/BasicClasses.R,
>> lines 524 ff has the following comment block
>>
>> | .OldClassesPrototypes is a list of S3 classes for which prototype
>> | objects are known & reasonable. The classes will reappear in
>> | .OldClassesList, but will have been initialized first in
>> | .InitBasicClasses. NB: the methods package will NOT set up
>> | prototypes for S3 classes except those in package base and for "ts"
>> | (and would rather not do those either). The package that owns the
>> | S3 class should have code to call setOldClass in its
>> | initialization.
>>
>> So, when John Chambers wrote this, he envisioned that the
>> 'stats' package would do "the correct thing" for its own classes.
>> OTOH, as history went, the stats package was never allowed to
>> depend on methods.
>> There are many other S3 classes from 'stats' which also end up
>> similarly, being defined via setOldClass() and that itself
>> produces a VIRTUAL class.
>> Also, another part of the (R source) comment above is no longer
>> quite accurate, e.g., "data.frame" is in .OldClassesPrototypes
>> but not in .OldClassesList ...
>>
>> As I do agree that "formula" is much more basic than these other classes,
>> I'm currently looking at tweaks to the methods (and stats) code,
>> to get this to work as indeed - you mentioned above - we
>> already allow "empty S3 formula" objects anyway.
>>
>> ... half an hour later : Indeed, I've been able to use the above
>> information
>> such that new("formula") and new("formula", y ~ x)
>> work.
>>
>> However, your code above now --- with my changes --- would fail :
>>
>> > setClass("A", representation(slot1="numeric", slot2="logical"))
>> > setClass("B", contains="A", representation(design="formula"))
>> > setClass("C", contains="B")
>> Error in reconcilePropertiesAndPrototype(name, slots, prototype,
>> superClasses, :
>> "B" is not eligible to be the data part of another class (must be a
>> basic class or a virtual class with no slots)
>> >
>>
Re: [Rd] Unexpected failure when calling new() with unnamed arg and
> Joshua Wiley
> on Thu, 8 Oct 2015 12:19:16 +1100 writes:
> Hi, I realize this is an old thread, but just wondering
> whether a conclusion was ever reached on this issue? I'm
> using formula(NULL) but it would be nice if default
> initialization worked for formula classes as well.
Well,
yes "of course", it was fixed quite a while ago ..
as I had ("almost") promissed (below).
Fixed only for R-devel though, e.g., because it potentially
requires package re-installation, etc.
Martin
> Cheers,
> Josh
> On Thu, May 14, 2015 at 8:13 AM, Hervé Pagès
> wrote:
>> Thanks Martin for looking into this. H.
>>
>>
>> On 05/13/2015 03:57 AM, Martin Maechler wrote:
>>
>>> Hervé Pagès
on Tue, 12 May 2015 15:18:42 -0700 writes:
>>>
>>> Hi,
>>>
>>> The man page for new() suggests that if 'a' is an object
>>> with slots
"slot1" and "slot2" and C is a class that extends the
class of 'a', then the 2 following calls should be
equivalent:
>>>
>>> new("C", a, ...)
new("C", slot1=a@slot1, slot2=a@slot2, ...)
>>>
>>> This is generally the case but I just ran into a
>>> situation where it's
not. In the following example the former fails while
the latter works:
>>>
>>> setClass("A", representation(slot1="numeric",
>>> slot2="logical"))
setClass("B", contains="A",
representation(design="formula")) setClass("C",
contains="B") a <- new("A", slot1=77, slot2=TRUE)
>>>
>>> new("C", a, design=x ~ y) # fails
new("C", slot1=a@slot1, slot2=a@slot2, design=x ~ y) #
works
>>>
>>> Note that new("B", a, design=x ~ y) works so the 3-level
>>> class
hierarchy is really needed in order to reproduce.
>>>
>>> Probably related to this, I also noted that new("B")
>>> and/or new("C")
return invalid objects:
>>>
>>> c <- new("C")
>>>
>>> validObject(c)
# Error in validObject(c) : # invalid class “C” object:
invalid object for slot "design" # in class "C": got
class "S4", should be or extend class "formula"
>>>
>>> is(c@design, "formula")
# [1] FALSE
>>>
>>> class(c@design)
# [1] "S4"
>>>
>>> Note that 'c' can be fixed:
>>>
>>> c@design <- formula(NULL)
>>>
>>> validObject(c)
# [1] TRUE
>>>
>>> Maybe something that the default "initialize" method
>>> should take care
of?
>>>
>>> Another singularity that is maybe at the root of all of
>>> this is that
the "formula" S4 class is virtual:
>>>
>>> showClass("formula")
# Virtual Class "formula" [package "methods"]
#
# Slots:
#
# Name: .S3Class # Class: character
#
# Extends: "oldClass"
>>>
>>> so a bare call to new("formula") fails:
>>>
>>> new("formula")
# Error in new("formula") : # trying to generate an
object from a virtual class ("formula")
>>>
>>> Shouldn't new("formula") just return an "empty" S3
>>> formula (like
formula(NULL) does), in the same way that
new("integer") returns an empty ordinary integer
vector?
>>>
>>> Interesting .. and at least worth following.
>>>
>>> One problem and historical reason for the current setup
>>> seems that the "formula" S3 class is not from 'base' but
>>> 'stats' :
>>>
>>> R's source, src/library/methods/R/BasicClasses.R, lines
>>> 524 ff has the following comment block
>>>
>>> | .OldClassesPrototypes is a list of S3 classes for
>>> which prototype | objects are known & reasonable. The
>>> classes will reappear in | .OldClassesList, but will
>>> have been initialized first in | .InitBasicClasses. NB:
>>> the methods package will NOT set up | prototypes for S3
>>> classes except those in package base and for "ts" | (and
>>> would rather not do those either). The package that
>>> owns the | S3 class should have code to call setOldClass
>>> in its | initialization.
>>>
>>> So, when John Chambers wrote this, he envisioned that
>>> the 'stats' package would do "the correct thing" for its
>>> own classes. OTOH, as history went, the stats package
>>> was never allowed to depend on methods. There are many
>>> other S3 classes from 'stats' which also end up
>>> similarly, being defined via setOldClass() and that
>>> itself produces a VIRTUAL class. Also, another part of
>>> the (R source) comment above is no longer quite
>>> accura
Re: [Rd] Unexpected failure when calling new() with unnamed arg and
Hi Martin,
Thanks and apologies for not seeing that. I had checked NEWS but not tried
it in R devel.
Thanks again.
Josh
On Thu, Oct 8, 2015 at 10:03 PM, Martin Maechler wrote:
> > Joshua Wiley
> > on Thu, 8 Oct 2015 12:19:16 +1100 writes:
>
> > Hi, I realize this is an old thread, but just wondering
> > whether a conclusion was ever reached on this issue? I'm
> > using formula(NULL) but it would be nice if default
> > initialization worked for formula classes as well.
>
> Well,
> yes "of course", it was fixed quite a while ago ..
> as I had ("almost") promissed (below).
>
> Fixed only for R-devel though, e.g., because it potentially
> requires package re-installation, etc.
>
> Martin
>
> > Cheers,
> > Josh
>
>
> > On Thu, May 14, 2015 at 8:13 AM, Hervé Pagès
> > wrote:
>
> >> Thanks Martin for looking into this. H.
> >>
> >>
> >> On 05/13/2015 03:57 AM, Martin Maechler wrote:
> >>
> >>> Hervé Pagès
> on Tue, 12 May 2015 15:18:42 -0700 writes:
>
> >>>
> >>> Hi,
>
> >>>
> >>> The man page for new() suggests that if 'a' is an object
> >>> with slots
> "slot1" and "slot2" and C is a class that extends the
> class of 'a', then the 2 following calls should be
> equivalent:
>
> >>>
> >>> new("C", a, ...)
> new("C", slot1=a@slot1, slot2=a@slot2, ...)
>
> >>>
> >>> This is generally the case but I just ran into a
> >>> situation where it's
> not. In the following example the former fails while
> the latter works:
>
> >>>
> >>> setClass("A", representation(slot1="numeric",
> >>> slot2="logical"))
> setClass("B", contains="A",
> representation(design="formula")) setClass("C",
> contains="B") a <- new("A", slot1=77, slot2=TRUE)
>
> >>>
> >>> new("C", a, design=x ~ y) # fails
> new("C", slot1=a@slot1, slot2=a@slot2, design=x ~ y) #
> works
>
> >>>
> >>> Note that new("B", a, design=x ~ y) works so the 3-level
> >>> class
> hierarchy is really needed in order to reproduce.
>
> >>>
> >>> Probably related to this, I also noted that new("B")
> >>> and/or new("C")
> return invalid objects:
>
> >>>
> >>> c <- new("C")
>
> >>>
> >>> validObject(c)
> # Error in validObject(c) : # invalid class “C” object:
> invalid object for slot "design" # in class "C": got
> class "S4", should be or extend class "formula"
>
> >>>
> >>> is(c@design, "formula")
> # [1] FALSE
>
> >>>
> >>> class(c@design)
> # [1] "S4"
>
> >>>
> >>> Note that 'c' can be fixed:
>
> >>>
> >>> c@design <- formula(NULL)
>
> >>>
> >>> validObject(c)
> # [1] TRUE
>
> >>>
> >>> Maybe something that the default "initialize" method
> >>> should take care
> of?
>
> >>>
> >>> Another singularity that is maybe at the root of all of
> >>> this is that
> the "formula" S4 class is virtual:
>
> >>>
> >>> showClass("formula")
> # Virtual Class "formula" [package "methods"]
> #
> # Slots:
> #
> # Name: .S3Class # Class: character
> #
> # Extends: "oldClass"
>
> >>>
> >>> so a bare call to new("formula") fails:
>
> >>>
> >>> new("formula")
> # Error in new("formula") : # trying to generate an
> object from a virtual class ("formula")
>
> >>>
> >>> Shouldn't new("formula") just return an "empty" S3
> >>> formula (like
> formula(NULL) does), in the same way that
> new("integer") returns an empty ordinary integer
> vector?
>
> >>>
> >>> Interesting .. and at least worth following.
> >>>
> >>> One problem and historical reason for the current setup
> >>> seems that the "formula" S3 class is not from 'base' but
> >>> 'stats' :
> >>>
> >>> R's source, src/library/methods/R/BasicClasses.R, lines
> >>> 524 ff has the following comment block
> >>>
> >>> | .OldClassesPrototypes is a list of S3 classes for
> >>> which prototype | objects are known & reasonable. The
> >>> classes will reappear in | .OldClassesList, but will
> >>> have been initialized first in | .InitBasicClasses. NB:
> >>> the methods package will NOT set up | prototypes for S3
> >>> classes except those in package base and for "ts" | (and
> >>> would rather not do those either). The package that
> >>> owns the | S3 class should have code to call setOldClass
> >>> in its | initialization.
> >>>
> >>> So, when John Chambers wrote this, he envisioned that
>
