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join_with_view's iteratorSection: 26.7.15.3 [range.join.with.iterator] Status: New Submitter: S. B. Tam Opened: 2024-03-23 Last modified: 2024-03-25
Priority: Not Prioritized
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Discussion:
join_with_view's iterator is defined in terms of variant, visit and get,
which implies that the iterator operations throw bad_variant_access if the underlying variant is
valueless-by-exception (which can happen if an underlying iterator has a throwing copy constructor).
variant is an implementation detail and shouldn't be exposed. It's confusing for users to
get bad_variant_access when user code does not deal with variant.
The spec of join_with_view is also inconsistent with concat_view as recently added to the
working draft by P2542R8. The latter has "it_.valueless_by_exception() is
false" as a precondition.
I believe that join_with_view should similarly require that inner_it_.valueless_by_exception()
is false for each iterator operation.
(FWIW, MSVC STL implements join_with_view with a trimmed-down version of variant, and having
to throw bad_variant_access causes a small maintenance burden.)
Proposed resolution: