Address iterator_category failing to compile for input iterators #27
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ednolan
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camio,
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steve-downey
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camio
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Nov 14, 2024
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Approved with one minor suggestion for the unit test.
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Should this behavior also apply when using |
The wording of P2727R4 states, with respect to the iterator_category type alias: "The nested type iterator_category is defined if and only if IteratorConcept is derived from forward_iterator_tag." Previously, this implementation had attempted to implement this using a class template detail::iter_cat, which had a specialization that contained an iterator_category member type alias which was only enabled if IteratorConcept was derived from std::forward_iterator_tag. However, the iter_category member type alias of iterator_interface itself was specified as detail::iter_cat</* ... */>>::iterator_category, which caused iterator_interface to simply fail to compile if IteratorConcept was not derived from forward_iterator_tag as detail::iter_cat's iterator_category was not found. This commit addresses the issue by removing the iterator_category member type alias from iterator_interface itself and making iterator_interface provide the member type alias by inheriting from detail::iter_cat, which satisfies the requirement in the wording. It also adds a reproducing unit test.
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The wording of P2727R4 states, with respect to the iterator_category type alias:
"The nested type iterator_category is defined if and only if IteratorConcept is derived from forward_iterator_tag."
Previously, this implementation had attempted to implement this using a class template detail::iter_cat, which had a specialization that contained an iterator_category member type alias which was only enabled if IteratorConcept was derived from
std::forward_iterator_tag. However, the iter_category member type alias of iterator_interface itself was specified as detail::iter_cat</* ... */>>::iterator_category, which caused iterator_interface to simply fail to compile if IteratorConcept was not derived from forward_iterator_tag as detail::iter_cat's iterator_category was not found.
This commit addresses the issue by removing the iterator_category member type alias from iterator_interface itself and making iterator_interface provide the member type alias by inheriting from detail::iter_cat, which satisfies the requirement in the wording. It also adds a reproducing unit test.