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Downcasting support added to quantity_cast (resolves #26)

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Mateusz Pusz
2019-11-09 14:42:06 +00:00
parent 4d1e225d9e
commit 2328a26992
2 changed files with 11 additions and 5 deletions
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13
src/include/units/quantity.h
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@ -157,29 +157,32 @@ namespace units {
} // namespace detail
template<Quantity To, typename U, typename Rep>
[[nodiscard]] constexpr To quantity_cast(const quantity<U, Rep>& q)
[[nodiscard]] constexpr auto quantity_cast(const quantity<U, Rep>& q)
requires same_dim<typename To::dimension, typename U::dimension>
{
using c_ratio = ratio_divide<typename U::ratio, typename To::unit::ratio>;
using c_rep = std::common_type_t<typename To::rep, Rep, intmax_t>;
using cast = detail::quantity_cast_impl<To, c_ratio, c_rep, c_ratio::num == 1, c_ratio::den == 1>;
using ret_dim = downcast<typename To::unit::dimension>;
using ret_unit = downcast<unit<ret_dim, typename To::unit::ratio>>;
using ret = quantity<ret_unit, typename To::rep>;
using cast = detail::quantity_cast_impl<ret, c_ratio, c_rep, c_ratio::num == 1, c_ratio::den == 1>;
return cast::cast(q);
}
template<Unit ToU, QuantityRep ToRep, typename U, typename Rep>
[[nodiscard]] constexpr quantity<ToU, ToRep> quantity_cast(const quantity<U, Rep>& q)
[[nodiscard]] constexpr auto quantity_cast(const quantity<U, Rep>& q)
{
return quantity_cast<quantity<ToU, ToRep>>(q);
}
template<Unit ToU, typename U, typename Rep>
[[nodiscard]] constexpr quantity<ToU, Rep> quantity_cast(const quantity<U, Rep>& q)
[[nodiscard]] constexpr auto quantity_cast(const quantity<U, Rep>& q)
{
return quantity_cast<quantity<ToU, Rep>>(q);
}
template<QuantityRep ToRep, typename U, typename Rep>
[[nodiscard]] constexpr quantity<U, ToRep> quantity_cast(const quantity<U, Rep>& q)
[[nodiscard]] constexpr auto quantity_cast(const quantity<U, Rep>& q)
{
return quantity_cast<quantity<U, ToRep>>(q);
}

3
test/unit_test/static/quantity_test.cpp
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@ -269,6 +269,9 @@ namespace {
// quantity_cast
static_assert(std::is_same_v<decltype(quantity_cast<unit<length, ratio<1>>>(2km))::unit, metre>);
static_assert(std::is_same_v<decltype(quantity_cast<unit<dimension<units::exp<base_dim_length, 1>>, ratio<1>>>(2km))::unit, metre>);
// static_assert(quantity_cast<int>(2km).count() == 2000); // should not compile
static_assert(quantity_cast<quantity<metre, int>>(2km).count() == 2000);
static_assert(quantity_cast<quantity<kilometre, int>>(2000m).count() == 2);