[Rd] Internal flag for S4 objects

[Uwe Ligges]

John Chambers wrote:
> A recent revision (svn version 39077) has introduced an internal flag (a 
> bit in the C structure) that is turned on by the code that generates 
> objects from an S4 class.
> 
> There are corresponding tests for an S4 object, isS4() in R and 
> IS_S4_OBJECT() in C.  These are fast and reliable, and should replace 
> any heuristic tests previously used.
> 
> The tests are not currently used widely, but in the future could be 
> combined with some of the other recent changes to improve reliability 
> and efficiency of computations with S4 objects.  Most such changes are 
> more likely for 2.5.x than 2.4.0.
> 
> S4 objects in saved sessions and other binary files will not have the 
> bit set, so they should be regenerated.  A likely symptom that you have 
> not done so is that the objects will not print automatically with the 
> standard S4 method, because the internal code now checks for an S4 
> object before dispatching show().
> 
> John

Dear R-devel testers under Windows,

this means that I won't upload the newly built Windows binary packages 
right now, but I will rebuild all of them again under current R-devel 
tomorrow. They won't appear on CRAN master before Wednesday. In the 
meantime, the link to R-2.3.x packages will remain active and some 
packages simply won't work.

Best,
Uwe Ligges