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Merged
saki7 merged 1 commit into from
Oct 1, 2026
Merged

Add more narrowing utils #102

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38 changes: 38 additions & 0 deletions include/iris/type_traits.hpp
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Original file line number Diff line number Diff line change
Expand Up @@ -314,6 +314,24 @@ struct is_convertible_without_narrowing<From, To>
template<class From, class To>
inline constexpr bool is_convertible_without_narrowing_v = is_convertible_without_narrowing<From, To>::value;

template<class T, class U>
struct is_assignable_without_narrowing : std::false_type
{};

template<class T, class U>
requires
std::is_assignable_v<T, U> &&
(
!std::is_scalar_v<std::remove_reference_t<T>> ||
is_convertible_without_narrowing_v<U, std::remove_reference_t<T>>
)
struct is_assignable_without_narrowing<T, U>
: std::true_type
{};

template<class T, class U>
inline constexpr bool is_assignable_without_narrowing_v = is_assignable_without_narrowing<T, U>::value;

// ----------------------------------------------

namespace detail {
Expand Down Expand Up @@ -552,6 +570,26 @@ struct no_narrowing_resolution<
template<class T, class... Ts>
struct no_narrowing_resolution : detail::no_narrowing_resolution<void, T, Ts...> {};

template<std::size_t I, class T>
struct conversion_overload
{
static std::integral_constant<std::size_t, I> select(T); // not defined
};

template<class... Overloads>
struct conversion_overloads : Overloads...
{
using Overloads::select...;
};

template<class Overloads, class U>
concept conversion_resolves = requires { Overloads::select(std::declval<U>()); };

template<class Overloads, class U, std::size_t I>
concept conversion_selects = requires {
{ Overloads::select(std::declval<U>()) } -> std::same_as<std::integral_constant<std::size_t, I>>;
};

// ----------------------------------------------

namespace detail {
Expand Down
32 changes: 32 additions & 0 deletions test/narrowing.cpp
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Expand Up @@ -425,3 +425,35 @@ TEST_CASE("is_assignable_without_any_narrowing", "[type_traits]")

STATIC_CHECK(!iris::is_assignable_without_any_narrowing_v<std::string&, char>); // initializer-list assignment
}

TEST_CASE("is_assignable_without_narrowing", "[type_traits]")
{
STATIC_CHECK(iris::is_assignable_without_narrowing_v<int&, int>);
STATIC_CHECK(iris::is_assignable_without_narrowing_v<long long&, int>);
STATIC_CHECK(!iris::is_assignable_without_narrowing_v<int&, long long>);
STATIC_CHECK(!iris::is_assignable_without_narrowing_v<double&, long long>);
STATIC_CHECK(!iris::is_assignable_without_narrowing_v<bool&, int*>);
STATIC_CHECK(!iris::is_assignable_without_narrowing_v<int&, to_long_long>); // after the conversion function
STATIC_CHECK(!iris::is_assignable_without_narrowing_v<int const&, int>);

// a class takes the value as the parameter of its assignment operator
STATIC_CHECK(iris::is_assignable_without_narrowing_v<port&, long long>);
STATIC_CHECK(iris::is_assignable_without_narrowing_v<assign_int&, long long>);
STATIC_CHECK(!iris::is_assignable_without_narrowing_v<assign_int&, std::string>);
}

TEST_CASE("conversion_overloads", "[type_traits]")
{
using int_or_long_long = iris::conversion_overloads<iris::conversion_overload<3, int>, iris::conversion_overload<5, long long>>;
STATIC_CHECK(iris::conversion_selects<int_or_long_long, int, 3>);
STATIC_CHECK(iris::conversion_selects<int_or_long_long, long long, 5>);
STATIC_CHECK(!iris::conversion_selects<int_or_long_long, int, 5>);
STATIC_CHECK(iris::conversion_selects<int_or_long_long, short, 3>); // a promotion
STATIC_CHECK(!iris::conversion_resolves<int_or_long_long, unsigned>); // ambiguous: both are conversions
STATIC_CHECK(!iris::conversion_resolves<int_or_long_long, std::string>);

using port_only = iris::conversion_overloads<iris::conversion_overload<0, port>>;
STATIC_CHECK(iris::conversion_selects<port_only, long long, 0>); // no narrowing check

STATIC_CHECK(!iris::conversion_resolves<iris::conversion_overloads<>, int>);
}
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