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Materialize recursive_wrapper<T> instead of T when possible#12

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saki7 merged 1 commit intomainfrom
materialize-recursive-wrapper
Feb 7, 2026
Merged

Materialize recursive_wrapper<T> instead of T when possible#12
saki7 merged 1 commit intomainfrom
materialize-recursive-wrapper

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@saki7 saki7 commented Feb 7, 2026 •
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Uses the functionality implemented in iris-cpp/iris#18

This PR solves the issue described in:

x4/include/iris/x4/traits/variant_traits.hpp

Lines 46 to 65 in 23686c5

template<class Attr, class First, class... Rest>
struct variant_find_substitute_impl<Attr, First, Rest...>
{
using type = std::conditional_t<
is_substitute_v<Attr, iris::unwrap_recursive_type<First>>,
// Given some type `T`, when both `T` and `recursive_wrapper<T>` is seen
// during attribute resolution, X4 should ideally materialize the latter
// because:
// - It means that the user has supplied at least one explicit type
// (i.e. exposed attribute type, possibly a rule attribute type) that
// is `recursive_wrapper<T>`, and
// - constructing `T` and then moving it to `recursive_wrapper<T>`
// involves copying from stack to heap.
//
First, // no need to unwrap due to the reason described above
typename variant_find_substitute_impl<Attr, Rest...>::type
>;
};

@saki7 saki7 self-assigned this Feb 7, 2026
@saki7 saki7 added the enhancement New feature or request label Feb 7, 2026
@saki7 saki7 merged commit 97f2a08 into main Feb 7, 2026
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@saki7 saki7 deleted the materialize-recursive-wrapper branch February 7, 2026 15:44
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