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

[Jiefei Wang]

Hi all,

By looking at the implementation of R's wrapper. I found a function `
R_altrep_inherits` that can check whether an object belongs to an ALTREP
class. Even though it is a little different from what I am looking for, but
it should be satisfactory for my purpose. I will suspect there is no such
function in R to get the class of an ALTREP object for the SEXP struct is
very compact and this less-important information might not be stored when
an ALTREP object is created.

Best,
Jiefei

On Mon, Oct 19, 2020 at 8:37 PM Jiefei Wang <szwjf08 using gmail.com> wrote:

> 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 using 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 Dénes Tóth <toth.denes using 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 using 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
>> > >>
>> > >>          [[alternative HTML version deleted]]
>> > >>
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>>
>

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