#[doc(hidden)]pub unsafe fn materialized_altrep_data2(x: SEXP) -> Option<SEXP>Expand description
Return the bridge’s R vector cache, if materialization has started.
Bridge-generated classes reserve data2 for a vector of the ALTREP’s type.
Once present, its values are the vector’s: read them, not the Rust data.
A string cache can be partial: slots not computed yet are C NULL, so
read it through the string Elt callback, never directly.
§Safety
x must be a live ALTREP using the bridge’s data2 convention, on R’s thread.