[libcxx-commits] [libcxx] [libc++] Avoid type-punning between __hash_value_type and pair (PR #143501)

[Louis Dionne via libcxx-commits]

================
@@ -845,6 +861,22 @@ public:
     return __emplace_unique(std::forward<_Pp>(__x));
   }
 
+  template <class _ValueT = _Tp, __enable_if_t<__is_hash_value_type<_ValueT>::value, int> = 0>
----------------
ldionne wrote:

As a follow-up refactoring, I would encourage something like this:

```c++
static constexpr bool __is_map_like = __is_hash_value_type<_Tp>::value;
static constexpr bool __is_set_like = !__is_map_like; // if desired

// Then:
template <bool _MapLike = __is_map_like, __enable_if_t<_MapLike, int> = 0>
void __insert_whatever(...) { ... }

template <bool _SetLike = __is_set_like, __enable_if_t<_SetLike, int> = 0>
void __insert_whatever(...) { ... }
```

That is equivalent but IMO easier to understand.

https://github.com/llvm/llvm-project/pull/143501