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S4SXP type vs S4 object bit?

4 messages · Travers Ching, Michael Lawrence, Jiefei Wang

Original
Travers Ching
# 
I'm trying to understand the R internals a bit better and reading over the
documentation.

I see that there is a bit related to whether an object is S4
(S4_OBJECT_MASK), and also the object type S4SXP (25).  The documentation
makes clear that these two things aren't the same.

But in practice, will the S4-bit and object type ever disagree for S4
objects?  I know that one can set the bit manually in C; are there any
practical applications for doing so?

Thank you
Travers
1 day later
Michael Lawrence
# 
Yes, any object of a class that derives from a basic type, like an
atomic vector for example, will be of the basic SEXP type, with the S4
bit set. This means that a class can extend "integer" and objects of
that class can be treated as any ordinary integer vector. S4SXP is
only for objects that do not derive from another basic type.

Michael
On Tue, Oct 22, 2019 at 1:28 AM Travers Ching <traversc at gmail.com> wrote:

  
    

      
      
    

  


  


      

    

    

      
      

        


  

        

      Jiefei Wang
    

    

      
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Hi Travers,

Just an additional remarks to Michael's answer, if your S4 class inherits
from R's basic types, say integer, the resulting object will be an INTSXP.
If your S4 class does not inherit from any class, it will be an S4SXP. You
can think about this question from the object-oriented framework: If one
class inherits the integer class, what should R do to make all the integer
related functions compatible with the new class at C level?

Best,
Jiefei

        
On Tue, Oct 22, 2019 at 4:28 AM Travers Ching <traversc at gmail.com> wrote:

        

            

      
      
      
    

        

      
      
    

        

  
  


  


      

    

    

      
      

        


  

        

      Travers Ching
    

    

      
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Thanks you Jiefei and Michael!

Travers

        
On Tue, Oct 22, 2019 at 8:14 AM Wang Jiefei <szwjf08 at gmail.com> wrote: