12 - External Pointers

In cpp4r, you can use external_pointer. In Rcpp, you can use XPtr to create external pointers. These have significantly different syntax, and cpp4r does not provide an attr method for external pointers.

For example, the cpp11tesseract package defines:

typedef cpp4r::external_pointer<tesseract::TessBaseAPI, tess_finalizer> TessPtr;

You can then call TessPtr with:

TessPtr ptr(api);
return ptr;

As a result, the R equivalent that the OCR C++ function verifies that the engine is such that the following is true:

stopifnot(inherits(engine, "externalptr"))

The equivalent tesseract package, which uses Rcpp, defines:

typedef Rcpp::XPtr<tesseract::TessBaseAPI, Rcpp::PreserveStorage, tess_finalizer, true> TessPtr;

You can then call TessPtr with:

TessPtr ptr(api);
ptr.attr("class") = Rcpp::CharacterVector::create("tesseract");
return ptr;

Similarly, the Rcpp version checks the engine with:

stopifnot(inherits(engine, "tesseract"))

These binaries (installable software) and packages are in development.
They may not be fully stable and should be used with caution. We make no claims about them.
Health stats visible at Monitor.