Is there any way to check the class of an ALTREP?

Thank Denes for the clarification, glad to see my package got one citation
from my own question:) Also, thank Benjamin
for sending many useful documents.

Actually, the question is related to the SharedObject package that
Benjamin has pointed to. I wanna
avoid sharing an object that has already been shared, so I need to check
whether an object is an ALTREP
that is defined in my package. Since the ALTREP definition involves an `
R_altrep_class_t` object and a
 class name, I will expect to see a method defined in R to retrieve such
information. I hope this can clarify my question.

Best,
Jiefei

On Mon, Oct 19, 2020 at 5:38 PM Benjamin Christoffersen <
boennecd at gmail.com> wrote:

You happened to send a link which points to the OP's own package :) I
think Jiefei would like to know how one can "officially" determine if an
arbitrary ALTERP object belongs to a class that he owns.

Argh, I am sorry! I did not notice that. My best bet for what I
thought the question was is section 1.1.2 of R Internals where they
note that: `unsigned int alt : 1; /* is this an ALTREP object? */`

This is also what the ALTREP macro checks. However, I also did not
notice the "... if an ALTREP object is from my package" part. I am
sorry.

Sincerely Yours,
Benjamin

Den man. 19. okt. 2020 kl. 11.25 skrev D?nes T?th <toth.denes at kogentum.hu

:

Benjamin,

You happened to send a link which points to the OP's own package :) I
think Jiefei would like to know how one can "officially" determine if an
arbitrary ALTERP object belongs to a class that he owns.

Regards,
Denes


On 10/19/20 10:22 AM, Benjamin Christoffersen wrote:

It seems as if you can you use the ALTREP macro as done in this
package:

https://github.com/Jiefei-Wang/SharedObject/blob/804b6ac58c63a4bae95343ab43e8b1547b07ee6b/src/C_interface.cpp#L185

and in base R:

https://github.com/wch/r-source/blob/54fbdca9d3fc63437d9e697f442d32732fb4f443/src/include/Rinlinedfuns.h#L118

The macro is defined here in Rinternals.h:

https://github.com/wch/r-source/blob/abb550c99b3927e5fc03d12f1a8e7593fddc04d2/src/include/Rinternals.h#L325

Den man. 19. okt. 2020 kl. 10.13 skrev Jiefei Wang <szwjf08 at gmail.com

:

Hi all,

I would like to determine if an ALTREP object is from my package, I

see

there is a function `ALTREP_CLASS` defined in RInternal.h but its

return

value is neither a `R_altrep_class_t` object nor an STRSXP

representing a

class name. I do not know how to correctly use it. Any suggestions?

Thanks,
Jiefei

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