slots of type "double"

What's the proposal here?  To eliminate "double" as a class?  No objection

from this corner.  As I remember, it was put in early in the implementation 
of methods, when I was confused about what R intended in this area (well, I'm 
not totally unconfused even now).

If this is the proposal, we could implement it in r-devel and see if there 
are complaints.

Prof Brian Ripley wrote:

On Tue, 13 Nov 2007, Simon Urbanek wrote:

On Nov 13, 2007, at 3:36 AM, hpages at fhcrc.org wrote:

Any idea why S4 doesn't allow slots of type "double"?

Type (as in storage type and "double" is a storage type) has nothing
to do with classes. You cannot create slots for types, only for classes.

Unfortunately not in the world of the 'methods' package (which seems to 
differ here from the Green Book and S-PLUS).  There's a basic class 
"double" (and also "single") defined in BasicClasses.R.  It say:

getClass("double")

No Slots, prototype of class "numeric"

Extends: "vector", "numeric"

getClass("numeric")

No Slots, prototype of class "numeric"

Extends: "vector"

Known Subclasses: "double", "integer"

So it is an otherwise unspecified subclass of "numeric".

Now when you do

a <- new("numeric", pi)
a

[1] 3.141593

class(a)

[1] "numeric"

you are in fact calling class() on a REALSXP, and that is set up to report 
"numeric" (the implicit class comes from mode not type, except for 
"integer").

Anther area of confusion is that as.numeric, as.double and as.real are 
three names for the same thing, but is.numeric and is.double are not the 
same.  So we end up with

x <- 1:3
is.numeric(x)

[1] TRUE

identical(x, as.numeric(x))

[1] FALSE

x <- pi
is.numeric(x)

[1] TRUE

identical(x, as.numeric(x))

[1] TRUE

Basically I think class() is wrong (it should use "double"), but it was not 
my choice and it was presumably done to agree with the Green Book.

I agree that it would be best to remove the "double" and "single" S4 
classes.  At least in the version of S-PLUS I have left, "double" does not 
exist -- "single" does but is a distinct storage type.

setClass("A", representation(a="double"))

 Error in makePrototypeFromClassDef(properties, ClassDef, immediate,
where) :
   in making the prototype for class "A" elements of the prototype
failed to
match the corresponding slot class: a (class ?double? )

"numeric", "integer", "character", "complex", "raw", etc... they all
work but "double" doesn't. Any reason for this strange exception?

AFAICS there is no way to create an object of the class "double" (save
for 'faking' it by creating an informal S3 object), so such definition
is useless. And given this fact, even the internal code is unable to
create it, so it doesn't match the signature. Note:

a=new("double")
class(a)

[1] "numeric"

is(a,"double")

[1] FALSE

I think it comes from the fact that there is an S4 definition for the
class "double" which is not valid. That is probably a bug and the
class definition should be removed.

Cheers,
Simon