Revert is_assignable_without_narrowing related change

iris-cpp · yaito3014 · Mar 11, 2026 · Mar 12, 2026 · Mar 12, 2026 · Mar 12, 2026
commit 8a4f0528f463497fd7fb2a75f11e9ebe63ac3db2
diff --git a/include/iris/type_traits.hpp b/include/iris/type_traits.hpp
@@ -241,29 +241,6 @@ template<class From, class To>
 inline constexpr bool is_convertible_without_narrowing_v = is_convertible_without_narrowing<From, To>::value;
 
 
-// is_assignable_without_narrowing<Dest, Source>
-//
-// True when `Dest = Source` is valid AND does not involve a narrowing conversion.
-//
-// The arithmetic guard is intentional: narrowing conversions are only defined for
-// arithmetic types ([dcl.init.list]), and the underlying `is_convertible_without_narrowing`
-// uses brace-initialization (`To[]{from}`) which may select a different construction
-// path than what `is_assignable` tests (e.g. initializer_list hijacking). Restricting
-// the narrowing check to arithmetic Dest avoids false rejections for non-arithmetic
-// types where the brace-init semantics diverge from assignment semantics.
-template<class Dest, class Source>
-struct is_assignable_without_narrowing
-    : std::bool_constant<
-        std::is_assignable_v<Dest, Source> &&
-        (!std::is_arithmetic_v<std::remove_reference_t<Dest>> ||
-         is_convertible_without_narrowing_v<std::remove_cvref_t<Source>, std::remove_reference_t<Dest>>)
-    >
-{};
-
-template<class Dest, class Source>
-inline constexpr bool is_assignable_without_narrowing_v = is_assignable_without_narrowing<Dest, Source>::value;
-
-
 namespace detail {
 
 template<std::size_t I, class Ti>

diff --git a/test/type_traits.cpp b/test/type_traits.cpp
@@ -137,50 +137,6 @@ TEST_CASE("is_convertible_without_narrowing")
 }
 
 
-TEST_CASE("is_assignable_without_narrowing")
-{
-    // Non-narrowing: same type
-    STATIC_CHECK(iris::is_assignable_without_narrowing_v<int&, int>);
-    STATIC_CHECK(iris::is_assignable_without_narrowing_v<double&, double>);
-
-    // Non-narrowing: widening
-    STATIC_CHECK(iris::is_assignable_without_narrowing_v<long long&, int>);
-    STATIC_CHECK(iris::is_assignable_without_narrowing_v<double&, float>);
-    STATIC_CHECK(iris::is_assignable_without_narrowing_v<int&, short>);
-
-    // Narrowing: lossy conversions
-    STATIC_CHECK(!iris::is_assignable_without_narrowing_v<int&, long long>);
-    STATIC_CHECK(!iris::is_assignable_without_narrowing_v<short&, int>);
-    STATIC_CHECK(!iris::is_assignable_without_narrowing_v<float&, double>);
-    STATIC_CHECK(!iris::is_assignable_without_narrowing_v<int&, float>);
-    STATIC_CHECK(!iris::is_assignable_without_narrowing_v<float&, int>);
-
-    // Signed/unsigned mismatch
-    STATIC_CHECK(!iris::is_assignable_without_narrowing_v<int&, unsigned>);
-    STATIC_CHECK(!iris::is_assignable_without_narrowing_v<unsigned&, int>);
-
-    // Non-arithmetic dest: narrowing not checked (trusts user-defined conversion)
-    STATIC_CHECK(iris::is_assignable_without_narrowing_v<std::string&, const char*>);
-    STATIC_CHECK(iris::is_assignable_without_narrowing_v<convertible_from_int&, int>);
-
-    // Not assignable at all
-    STATIC_CHECK(!iris::is_assignable_without_narrowing_v<not_convertible_from_int&, int>);
-    STATIC_CHECK(!iris::is_assignable_without_narrowing_v<int&, std::string>);
-
-    // Non-arithmetic dest with explicit ctor + assignment operator.
-    // Without the arithmetic guard, is_assignable_without_narrowing would
-    // incorrectly return false because is_convertible_without_narrowing
-    // rejects explicit conversions (brace-init uses copy-list-init).
-    STATIC_CHECK(std::is_assignable_v<explicit_from_int&, int>);
-    STATIC_CHECK(!iris::is_convertible_without_narrowing_v<int, explicit_from_int>);
-    STATIC_CHECK(iris::is_assignable_without_narrowing_v<explicit_from_int&, int>);
-
-    // Verify the "false" implementation (without arithmetic guard) breaks here:
-    // it incorrectly rejects this valid, non-narrowing assignment.
-    STATIC_CHECK(!broken_is_assignable_without_narrowing<explicit_from_int&, int>::value);
-}
-
-
 TEST_CASE("specialization_of")
 {
     STATIC_CHECK(iris::is_ttp_specialization_of_v<tuple<>, tuple>);