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Avoid instantiation of TupleLike on completely irrelevant context #88

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Merged
saki7 merged 1 commit into from
Aug 15, 2026
Merged

Avoid instantiation of TupleLike on completely irrelevant context #88

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30 changes: 24 additions & 6 deletions include/iris/alloy/traits.hpp
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Original file line number Diff line number Diff line change
Expand Up @@ -187,12 +187,30 @@ struct basic_common_reference_impl<TTuple, UTuple, TQual, UQual, std::index_sequ

} // iris::alloy

template<iris::alloy::TupleLike TTuple, iris::alloy::TupleLike UTuple, template<class> class TQual, template<class> class UQual>
requires (iris::is_ttp_specialization_of_v<TTuple, iris::alloy::tuple> ||
iris::is_ttp_specialization_of_v<UTuple, iris::alloy::tuple>) &&
(iris::alloy::tuple_size_v<TTuple> == iris::alloy::tuple_size_v<UTuple>)
// Note: We can't directly specify the concept `TupleLike` in the
// declaration of the template parameter because it would invoke
// the `TupleLike` check for virtually ANY types whenever the
// *primary* template of `std::basic_common_reference` is instantiated.
//
// Doing so would produce some hard errors on completely irrelevant
// context; for example, calling `std::map<T, U>{}.rbegin()` would
// inevitably *check* `TupleLike` for `std::pair<T const, U>` thus
// leads to instantiation of `getter_of`. Then if the instantiation
// yields hard error for some reason, the error is propagated to the
// caller in SFINAE-unfriendly context.
template<class TTuple, class UTuple, template<class> class TQual, template<class> class UQual>
requires
(
iris::is_ttp_specialization_of_v<TTuple, iris::alloy::tuple> ||
iris::is_ttp_specialization_of_v<UTuple, iris::alloy::tuple>
) &&
iris::alloy::TupleLike<TTuple> && iris::alloy::TupleLike<UTuple> &&
(iris::alloy::tuple_size_v<TTuple> == iris::alloy::tuple_size_v<UTuple>)
struct std::basic_common_reference<TTuple, UTuple, TQual, UQual>
: iris::alloy::detail::basic_common_reference_impl<TTuple, UTuple, TQual, UQual,
std::make_index_sequence<iris::alloy::tuple_size_v<TTuple>>> {};
: iris::alloy::detail::basic_common_reference_impl<
TTuple, UTuple, TQual, UQual,
std::make_index_sequence<iris::alloy::tuple_size_v<TTuple>>
>
{};

#endif
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