[libcxx-commits] [libcxx] [libc++] P3798R1: The unexpected in std::expected (PR #204826)

[Hristo Hristov via libcxx-commits]

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@@ -825,6 +825,10 @@ class expected : private __expected_base<_Tp, _Err> {
 
   [[nodiscard]] _LIBCPP_HIDE_FROM_ABI constexpr bool has_value() const noexcept { return this->__has_val(); }
 
+#  if _LIBCPP_STD_VER >= 29 
+  [[nodiscard]] _LIBCPP_HIDE_FROM_ABI constexpr bool has_error() const noexcept { return !this->has_value(); }
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Zingam wrote:

`[[nodiscard]]` needs a test.

`noexcept` needs a test, usually "static_assert(noexcept(exp.has_error()))` instead of declaring a concept.
Test return type with `std::same_as<bool> decltype(auto) error = exp.has_error()`.

You also need to update the `void` specialization here: https://github.com/llvm/llvm-project/blob/3c5f0c2d3e00a22a275f404bac29ce62c69d95d5/libcxx/include/__expected/expected.h#L1600 as seen in the Draft here: https://github.com/cplusplus/draft/pull/9127/changes


https://github.com/llvm/llvm-project/pull/204826