Function materialized_altrep_region 

#[doc(hidden)]
pub unsafe fn materialized_altrep_region<T: Copy>(
    data2: SEXP,
    start: usize,
    len: usize,
    out: &mut [T],
) -> usize

Read a region from a materialized atomic vector, without consulting data1.

Safety

data2 must be a live plain R vector with element layout T, on R’s thread.