[libcxx-commits] [libcxx] [libc++] P2944R3: Constrained comparisons - `optional` (PR #144249)

[A. Jiang via libcxx-commits]

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@@ -24,20 +24,23 @@ _LIBCPP_BEGIN_NAMESPACE_STD
 // and __is_core_convertible<immovable-type,immovable-type> is true in C++17 and later.
 
 template <class _Tp, class _Up, class = void>
-struct __is_core_convertible : false_type {};
+inline const bool __is_core_convertible_v = false;
 
 template <class _Tp, class _Up>
-struct __is_core_convertible<_Tp, _Up, decltype(static_cast<void (*)(_Up)>(0)(static_cast<_Tp (*)()>(0)()))>
-    : true_type {};
+inline const bool
+    __is_core_convertible_v<_Tp, _Up, decltype(static_cast<void (*)(_Up)>(0)(static_cast<_Tp (*)()>(0)()))> = true;
+
+template <class _Tp, class _Up>
+using __is_core_convertible _LIBCPP_NODEBUG = integral_constant<bool, __is_core_convertible_v<_Tp, _Up> >;
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frederick-vs-ja wrote:

Hmm, the difference between inheritance and aliasing seems to be laziness of instantiation. If it's confirmed that shortcut instantiation is not so that desired, we can even remove `__is_core_convertible` and consistently use `__is_core_convertible_v`. (The changes should belong to another PR, though.)

https://github.com/llvm/llvm-project/pull/144249