[libcxx-commits] [libcxx] [libc++] Implement P2988R12: `std::optional<T&>` (PR #155202)

[A. Jiang via libcxx-commits]

================
@@ -23,8 +23,7 @@ concept has_iterator_aliases = requires {
 
 static_assert(has_iterator_aliases<std::optional<int>>);
 static_assert(has_iterator_aliases<std::optional<const int>>);
-
-// TODO: Uncomment these once P2988R12 is implemented, as they would be testing optional<T&>
-
-// static_assert(!has_iterator_aliases<std::optional<int (&)[]>>);
-// static_assert(!has_iterator_aliases<std::optional<void (&)(int, char)>>);
+static_assert(has_iterator_aliases<std::optional<int&>>);
+static_assert(has_iterator_aliases<std::optional<const int&>>);
+static_assert(!has_iterator_aliases<std::optional<int (&)[1]>>);
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frederick-vs-ja wrote:

Looks like that we should achieve the following results, per the current resolution of [LWG4308](https://cplusplus.github.io/LWG/issue4308).
```suggestion
static_assert(has_iterator_aliases<std::optional<int (&)[1]>>);
static_assert(!has_iterator_aliases<std::optional<int (&)[]>>);
```
The product code needs to be correspondingly adjusted. We can do this in a following-up PR as LWG4308 is not formally accepted yet (but it will be soon).

https://github.com/llvm/llvm-project/pull/155202