[libcxx-commits] [PATCH] D101316: [libcxx][ranges] Add `random_access_{iterator, range}`.

[Christopher Di Bella via Phabricator via libcxx-commits]

cjdb added inline comments.


================
Comment at: libcxx/test/std/containers/views/span.iterators/iterator_concept_conformance.compile.pass.cpp:24
 static_assert(std::bidirectional_iterator<iterator>);
+static_assert(std::random_access_iterator<iterator>);
 static_assert(std::indirectly_writable<iterator, value_type>);
----------------
Quuxplusone wrote:
> zoecarver wrote:
> > Quuxplusone wrote:
> > > It only now occurs to me that it would be useful to verify `std::random_access_iterator<reverse_iterator>` as well.
> > > 
> > > To keep the tests simple, I think you should add `std::random_access_iterator<reverse_iterator>` only on the containers that are in fact random-access. If `!std::random_access_iterator<iterator>`, then I think we can safely call it obvious that `!std::random_access_iterator<reverse_iterator>`.
> > I think we decided as long as we're testing `std::reverse_iterator` it's ok not to test `vector::reverse_iterator` (and other reverse iterators that are known to be type aliases for `std::reverse_iterator`) because we know they're going to be the same. 
> > as long as we're testing `std::reverse_iterator`
> 
> Are you testing `std::reverse_iterator<std::vector<int>::iterator>`, though? Specifically I do think we should be testing `std::reverse_iterator<std::vector<int>::iterator>` (because it's a `__wrap_iter`) and `std::reverse_iterator<std::vector<bool>::iterator>` (because it's special). And personally I'd do it here, adding to the test for vector iterators (rather than, say, adding to the test for reverse_iterator).
> 
> It only now occurs to me that it would be useful to verify `std::random_access_iterator<reverse_iterator>` as well.
> 
> To keep the tests simple, I think you should add `std::random_access_iterator<reverse_iterator>` only on the containers that are in fact random-access. If `!std::random_access_iterator<iterator>`, then I think we can safely call it obvious that `!std::random_access_iterator<reverse_iterator>`.

This should be in the `reverse_iterator` conformance test, and can probably be just `reverse_iterator<reverse_iterator<int*>>`. This opinion is neutral for addition, strongly in favour for placement.

As for `__wrap_iter`/`vector<bool>::iterator`, I'm not convinced that's necessary, since the conformance checks confirms `reverse_iterator<some_random_access_iterator>` is a random-access iterator. This opinion is weakly-against/borderline neutral for addition and strongly in agreement with Arthur for placement.


Repository:
  rG LLVM Github Monorepo

CHANGES SINCE LAST ACTION
  https://reviews.llvm.org/D101316/new/

https://reviews.llvm.org/D101316