[libcxx-commits] [libcxx] [libc++] Avoid using **this to access the value stored in std::expected (PR #84840)

[A. Jiang via libcxx-commits]

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@@ -920,9 +920,9 @@ class expected : private __expected_base<_Tp, _Err> {
     requires is_constructible_v<_Err, _Err&>
   _LIBCPP_HIDE_FROM_ABI constexpr auto and_then(_Func&& __f) & {
     using _Up = remove_cvref_t<invoke_result_t<_Func, _Tp&>>;
-    static_assert(__is_std_expected<_Up>::value, "The result of f(**this) must be a specialization of std::expected");
+    static_assert(__is_std_expected<_Up>::value, "The result of f(value()) must be a specialization of std::expected");
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frederick-vs-ja wrote:

This may be a bit misleading as `value()` can be ill-formed (because the error type is not copyable) while monadic operations being well-formed. See also [LWG3938](https://cplusplus.github.io/LWG/issue3938) and [LWG3940](https://cplusplus.github.io/LWG/issue3940).

The resolution of [LWG3973](https://cplusplus.github.io/LWG/issue3973) uses _`val`_ (exposition-only member name). Perhaps we can use `val` or `__val()` (libc++-specific function name) in the error messages instead.

https://github.com/llvm/llvm-project/pull/84840