message: Random access iterator conformance
diff: @@ -491,7 +491,7 @@ struct CollectionIterator {
  return *this;
  }
  - friend ptrdiff_t operator-(CollectionIterator& lhs, CollectionIterator& rhs) noexcept
  + friend ptrdiff_t operator-(const CollectionIterator& lhs, const CollectionIterator& rhs) noexcept
  {
  return ptrdiff_t(lhs.m_ndx) - ptrdiff_t(rhs.m_ndx);
  }
  