Checking multiple inheritance of S4 objects using R's C API

On Feb 16, 2021, at 12:03 PM, Emre Gonulates <egonulates at gmail.com> wrote:

Hi,

Suppose I have the following two classes in R:


setClass("Person", representation(name = "character", age = "numeric"))
setClass("Employee", representation(boss = "Person"), contains = "Person")


I can successfully check inheritance in base R:


employee <- new("Employee", name = "Jack", age = 25)

inherits(employee, "Employee")
#> [1] TRUE
inherits(employee, "Person")
#> [1] TRUE


I could not achieve the same in Rcpp:


Rcpp::cppFunction('
void check_class(Rcpp::S4 x) {
 Rcout << "Class: " << as<std::string>(x.attr("class")) << std::endl;
 Rcout << "Rf_inherits(x, \\"Employee\\") : " << Rf_inherits(x,
"Employee") << std::endl;
 Rcout << "Rf_inherits(x, \\"Person\\")   : " << Rf_inherits(x, "Person")
<< std::endl;
 Rcout << "R_extends : " << R_extends(x, Rf_mkString("Person"),
R_GlobalEnv) << std::endl;
}')

check_class(employee)
#> Class: Employee
#> Rf_inherits(x, "Employee") : 1
#> Rf_inherits(x, "Person")   : 0
#> R_extends :
#> Error in extends(new("Employee", boss = new("Person", name =
character(0), : 'class1' must be the name of a class or a class definition


I expected `Rf_inherits(x, "Person")` to be true as well.

How can I check whether an object inherits from parent classes in R's C API?

Thanks,
Emre.


P.S. This question originally posted <a href="
https://stackoverflow.com/q/66201929/2275286">here</a>.

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