Function altrep_data2_as 

pub unsafe fn altrep_data2_as<T: TypedExternal>(
    x: SEXP,
) -> Option<ExternalPtr<T>>

Extract the ALTREP data2 slot as a typed ExternalPtr<T>.

Similar to altrep_data1_as, but for the data2 slot.

Safety

• x must be a valid ALTREP SEXP
• Must be called from the R main thread