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Implement apply with std 17 #2835

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Merged
merged 1 commit into from
Apr 2, 2025
+23 −22
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Implement apply with std 17 #2835

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39 changes: 20 additions & 19 deletions include/xtensor/utils/xutils.hpp
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Original file line number Diff line number Diff line change
Expand Up @@ -283,29 +283,30 @@ namespace xt
* apply implementation *
************************/

namespace detail
{
template <class R, class F, std::size_t I, class... S>
R apply_one(F&& func, const std::tuple<S...>& s) NOEXCEPT(noexcept(func(std::get<I>(s))))
{
return static_cast<R>(func(std::get<I>(s)));
}

template <class R, class F, std::size_t... I, class... S>
R apply(std::size_t index, F&& func, std::index_sequence<I...> /*seq*/, const std::tuple<S...>& s)
NOEXCEPT(noexcept(func(std::get<0>(s))))
{
using FT = std::add_pointer_t<R(F&&, const std::tuple<S...>&)>;
static const std::array<FT, sizeof...(I)> ar = {{&apply_one<R, F, I, S...>...}};
return ar[index](std::forward<F>(func), s);
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@spectre-ns spectre-ns Mar 30, 2025 •
edited
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Potential access violation if index > I - 1.

}
}

template <class R, class F, class... S>
inline R apply(std::size_t index, F&& func, const std::tuple<S...>& s)
NOEXCEPT(noexcept(func(std::get<0>(s))))
{
return detail::apply<R>(index, std::forward<F>(func), std::make_index_sequence<sizeof...(S)>(), s);
XTENSOR_ASSERT(sizeof...(S) > index);
return std::apply(
[&](const S&... args) -> R
{
auto f_impl = [&](auto&& self, auto&& i, auto&& h, auto&&... t) -> R
{
if (i == index)
{
return static_cast<R>(func(h));
}
if constexpr (sizeof...(t) > 0)
{
return self(self, std::size_t{i + 1}, t...);
}
return R{};
};
return f_impl(f_impl, std::size_t{0}, args...);
},
s
);
}

/***************************
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6 changes: 3 additions & 3 deletions test/test_xutils.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -104,16 +104,16 @@ namespace xt
TEST(utils, apply)
{
ASSERT_TRUE(foo(std::make_tuple(1, 2, 3)) == 2);
EXPECT_FALSE(noexcept(foo(std::make_tuple(1, 2, 3))));
static_assert(!noexcept(foo(std::make_tuple(1, 2, 3))));
auto func_ne = [](int i) noexcept
{
return i;
};
auto t = std::make_tuple(1, 2, 3);
#if (_MSC_VER >= 1910)
EXPECT_FALSE(noexcept(apply<int>(1, func_ne, t)));
static_assert(!noexcept(apply<int>(1, func_ne, t)));
#else
EXPECT_TRUE(noexcept(apply<int>(1, func_ne, t)));
static_assert(noexcept(apply<int>(1, func_ne, t)));
#endif
}

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