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fix: make the array overload of variables() deducible #78

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Merged
oberbichler merged 1 commit into from
Jul 26, 2026
Merged

fix: make the array overload of variables() deducible #78

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8 changes: 5 additions & 3 deletions include/hyperjet/hyperjet.h
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Original file line number Diff line number Diff line change
Expand Up @@ -578,12 +578,14 @@ class DDScalar {
return vars;
}

template <index T>
// std::array is sized by std::size_t, so T has to be as well or the size
// can never be deduced from the argument.
template <std::size_t T>
static std::conditional_t<TSize == Dynamic, std::vector<Type>,
std::array<Type, T>>
variables(const std::array<Scalar, T> &values) {
if constexpr (!is_dynamic()) {
static_assert(T == TSize);
static_assert(index(T) == TSize);
}

const index s = length(values);
Expand All @@ -595,7 +597,7 @@ class DDScalar {
}
return vars;
} else {
std::array<Type, TSize> vars;
std::array<Type, T> vars;
for (index i = 0; i < s; i++) {
vars[i] = variable(i, values[i], s);
}
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2 changes: 1 addition & 1 deletion python/src/common.h
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Expand Up @@ -93,7 +93,7 @@ template <typename T> auto bind(py::module &m, const std::string &name) {
.def_static(
"variables",
[](const std::array<typename T::Scalar, T::static_size()> &values) {
return T::template variables<T::static_size()>(values);
return T::variables(values);
},
"values"_a);
}
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40 changes: 40 additions & 0 deletions test/src/test.cpp
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Expand Up @@ -830,3 +830,43 @@ TEST_CASE("SScalar Hypot") {
REQUIRE(r2.d("y") == doctest::Approx(4.4400151526317840));
REQUIRE(r2.d("z") == doctest::Approx(2.4076700872634590));
}

// The C++ usage example from the README. Its values are pinned here so the
// example cannot silently stop compiling or start lying.

TEST_CASE("README example") {
auto [x, y] = DDScalar<2, double, 2>::variables(std::array{3.0, 6.0});

const auto f = (x * y) / (x - y);

REQUIRE(f.f() == doctest::Approx(-6.0));
REQUIRE(f.g(0) == doctest::Approx(-4.0));
REQUIRE(f.g(1) == doctest::Approx(1.0));

// the same computation as the Python quickstart, whose output the README
// shows as well
REQUIRE(f.h(0, 0) == doctest::Approx(-2.6666666666666667));
REQUIRE(f.h(0, 1) == doctest::Approx(1.3333333333333333));
REQUIRE(f.h(1, 1) == doctest::Approx(-0.6666666666666666));
}

TEST_CASE("Variables from an array") {
const auto s = DDScalar<2, double, 2>::variables(std::array{3.0, 6.0});

REQUIRE(s.size() == 2);
REQUIRE(s[0].f() == doctest::Approx(3.0));
REQUIRE(s[0].g(0) == doctest::Approx(1.0));
REQUIRE(s[0].g(1) == doctest::Approx(0.0));
REQUIRE(s[1].f() == doctest::Approx(6.0));
REQUIRE(s[1].g(0) == doctest::Approx(0.0));
REQUIRE(s[1].g(1) == doctest::Approx(1.0));

// the dynamic variant returns a vector, sized from the array
const auto d = DDScalar<2, double, Dynamic>::variables(std::array{3.0, 6.0});

REQUIRE(d.size() == 2);
REQUIRE(d[0].size() == 2);
REQUIRE(d[0].f() == doctest::Approx(3.0));
REQUIRE(d[0].g(0) == doctest::Approx(1.0));
REQUIRE(d[1].g(1) == doctest::Approx(1.0));
}
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