Tuple protocol for fixed-size span (P3786R2)#7
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Adds the three pieces from P3786R2: - std::tuple_size<span<T, N>> - integral_constant<size_t, N> - std::tuple_element<I, span<T, N>> - using type = T& - get<I>(span<T, N>) returning T&, in beman::span so ADL finds it for structured bindings All three are gated on N != dynamic_extent via constrained partial specialization, so std::tuple_size<span<T>> falls back to the undefined primary template and remains SFINAE-friendly for the tuple-like concept. Top-level cv on the span is handled automatically by the existing std::tuple_size<const T> / std::tuple_element<I, const T> partial specs. Six new tests cover tuple_size value, tuple_element returning references (including const-element-type and top-level-const cases), get returning a reference to the underlying element, structured bindings binding by reference, and the dynamic_extent SFINAE behaviour. Fixes #4
# Conflicts: # include/beman/span/span.hpp
Pure formatter output. Reflows the new tuple_size / tuple_element / get specializations and tightens up the SpanTuple tests under the .clang-format AlignConsecutiveDeclarations and ColumnLimit rules. Also picks up the at() test alignment carried in via the merge.
# Conflicts: # tests/beman/span/span.test.cpp
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coverage: 100.0%. remained the same — tuple-protocol-p3786r2 into main |
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Implements P3786R2 so fixed-size spans support the tuple protocol and structured bindings.
Three additions, per the paper:
std::tuple_size<span<T, N>>specialised tointegral_constant<size_t, N>.std::tuple_element<I, span<T, N>>withusing type = T&(a reference, since a span element lives outside the span).get<I>(span<T, N>)returningT&. Lives inbeman::spanso ADL picks it up forauto& [a, b, c] = s;.All three are gated on
N != dynamic_extentvia constrained partial specialisation. Forspan<T>(dynamic) the specialisations don't apply, sostd::tuple_size<span<T>>falls back to the undefined primary template — that's the SFINAE-friendly behaviour thetuple-likeconcept relies on.Top-level cv on the span itself (
const span<T, N>) is handled by the existingstd::tuple_size<const T>/std::tuple_element<I, const T>partial specialisations in the standard, so we don't need to do anything for that case.Six new tests:
tuple_size_vfor fixed extents including 0tuple_element_treturningT&/const T&/int&forconst span<int, N>get<I>returning a reference, with mutation visible through the underlying arrayLocal: 51/51 passing.
Fixes #4