Skip to contents

Native API

Source: R/native-api.R
native-api.Rd

S7 provides a stable native API for retrieving class definitions and reading properties.

Details

  • SEXP S7_get_class(SEXP object) returns the stored S7 class definition, or R_NilValue if there is none. Unlike S7_class(), it does not construct class specifications for base, S3, or S4 objects.

  • SEXP S7_get_prop(SEXP object, SEXP name) reads a property, including custom getters, as prop() does. name must be a character vector of length one containing a non-missing string.

C and C++

Add S7 to Imports and LinkingTo in DESCRIPTION. In NAMESPACE, add importFrom(S7, S7_class) and useDynLib(mypkg, .registration = TRUE).

In src/init.c, initialize the API and register the .Call routine:

#include <S7-init.h>

extern SEXP object_value(SEXP object);

static const R_CallMethodDef CallEntries[] = {
  {"object_value", (DL_FUNC) &object_value, 1},
  {NULL, NULL, 0}
};

void R_init_mypkg(DllInfo *dll) {
  S7_init_api();
  R_registerRoutines(dll, NULL, CallEntries, NULL, NULL);
  R_useDynamicSymbols(dll, FALSE);
  R_forceSymbols(dll, TRUE);
}

In src/value.c, define the routine that reads the value property:

#include <S7.h>

SEXP object_value(SEXP object) {
  SEXP name = PROTECT(Rf_mkString("value"));
  SEXP value = S7_get_prop(object, name);
  UNPROTECT(1);
  return value;
}

An R wrapper in the package can call .Call(object_value, object). Other C/C++ source files include <S7.h>. In C++ files, use extern "C" for the declaration and definition of object_value() and the definition of R_init_mypkg().

Other native bindings

Rust and other bindings can cache pointers from R_GetCCallable("S7", "S7_get_class") and R_GetCCallable("S7", "S7_get_prop") after loading S7, using the signatures above and the C calling convention.