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This patch introduces the internal helper type _IotaArray to simplify defining a pack of indices via a structured binding declaration: constexpr auto [...__is] = _IotaArray<N>; _IotaArray is a C-array for lowest overhead in terms of template instantiations. Non-GCC compilers that do not implement __integer_pack have a slightly higher overhead. libstdc++-v3/ChangeLog: * include/bits/utility.h (_IotaArray): Define. * testsuite/ext/iotaarray.cc: New test. Signed-off-by: Matthias Kretz <m.kretz@gsi.de>
21 lines
391 B
C++
21 lines
391 B
C++
// { dg-do compile { target c++26 } }
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#include <utility>
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#include <type_traits>
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template<auto N>
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void test()
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{
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constexpr auto [id0, ...ids] = std::_IotaArray<N>;
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static_assert( std::is_same_v<decltype(id0), const decltype(N)> );
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static_assert( sizeof...(ids) == N - 1 );
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static_assert( (id0 + ... + ids) == N*(N-1)/2 );
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}
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int main()
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{
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test<1>();
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test<4u>();
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test<8ull>();
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}
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