PL/R is not ALTREP aware

[mlt]

The following test code

create or replace function altrep_test() returns int[] as $$
  as.numeric( .Internal(mmap_file("postmaster.opts", "int", FALSE, FALSE, FALSE)) )
$$ language plr;

select cardinality(altrep_test());

create or replace function altrep_test2() returns int[] as $$
  .Internal(mmap_file("postmaster.opts", "int", FALSE, FALSE, FALSE))
$$ language plr;

select cardinality(altrep_test2());

will crash on the second test with

Error: cannot access data pointer for this mmaped vector
Fatal error: unable to initialize the JIT

Calls like INTEGER() and REAL() try to materialize objects (unless explicitly prohibited in the example above) whereas INTEGER_ELT and REAL_ELT won't at the expense of not being inlined in newer R.

All fast track copy code should check if (!ALTREP(rval)). Alternatively, I suggest to use corresponding xxx_ELT ALTREP-aware accessors with a small performance penalty. Since there are checks for NA anyway, we might as well just copy an element to avoid extra code complexity.

[davecramer]

closed lack of activity, please reopen if still relevant