From ripley at stats.ox.ac.uk  Tue Nov 13 19:19:02 2007
From: ripley at stats.ox.ac.uk (Prof Brian Ripley)
Date: Tue, 13 Nov 2007 18:19:02 +0000 (GMT)
Subject: [Rd] slots of type "double"
In-Reply-To: <4739E8F3.5040302@r-project.org>
References: <1194942985.4739620919f16@webmail.fhcrc.org>
	<2BBF01A3-5F39-4750-B42E-12605674F49E@r-project.org>
	<Pine.LNX.4.64.0711131448370.9317@gannet.stats.ox.ac.uk>
	<4739E8F3.5040302@r-project.org>
Message-ID: <Pine.LNX.4.64.0711131816130.11720@gannet.stats.ox.ac.uk>

On Tue, 13 Nov 2007, John Chambers wrote:

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

Eliminate "double" and "single".

> 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.

I was going to propose so after running some tests over CRAN/BioC (which 
will take a few hours).

Brian

> 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
>>> 
>>> ______________________________________________
>>> R-devel at r-project.org mailing list
>>> https://stat.ethz.ch/mailman/listinfo/r-devel
>>>
>>> 
>>
>>

-- 
Brian D. Ripley,                  ripley at stats.ox.ac.uk
Professor of Applied Statistics,  http://www.stats.ox.ac.uk/~ripley/
University of Oxford,             Tel:  +44 1865 272861 (self)
1 South Parks Road,                     +44 1865 272866 (PA)
Oxford OX1 3TG, UK                Fax:  +44 1865 272595



[Rd] slots of type "double"
Prof Brian Ripley