From 3d654f96d4c583c35e4f73aa8f11371730671534 Mon Sep 17 00:00:00 2001 From: Jonathan Wakely Date: Wed, 1 Nov 2023 14:28:55 +0000 Subject: [PATCH] libstdc++: Improve static assert messages for monadic operations The monadic operations for std::optional and std::expected make use of internal helper traits __is_optional nad __is_expected, which are not very user-friendly when shown in diagnostics. Add messages to the assertions explaining the problem more clearly. libstdc++-v3/ChangeLog: * include/std/expected (expected::and_then, expected::or_else): Add string literals to static assertions. * include/std/optional (optional::and_then, optional::or_else): Likewise. --- libstdc++-v3/include/std/expected | 64 +++++++++++++++++++++++-------- libstdc++-v3/include/std/optional | 24 +++++++++--- 2 files changed, 66 insertions(+), 22 deletions(-) diff --git a/libstdc++-v3/include/std/expected b/libstdc++-v3/include/std/expected index a796f0b6f27e..a176d4c3a780 100644 --- a/libstdc++-v3/include/std/expected +++ b/libstdc++-v3/include/std/expected @@ -843,8 +843,12 @@ namespace __expected and_then(_Fn&& __f) & { using _Up = __expected::__result<_Fn, _Tp&>; - static_assert(__expected::__is_expected<_Up>); - static_assert(is_same_v); + static_assert(__expected::__is_expected<_Up>, + "the function passed to std::expected::and_then " + "must return a std::expected"); + static_assert(is_same_v, + "the function passed to std::expected::and_then " + "must return a std::expected with the same error_type"); if (has_value()) return std::__invoke(std::forward<_Fn>(__f), _M_val); @@ -857,8 +861,12 @@ namespace __expected and_then(_Fn&& __f) const & { using _Up = __expected::__result<_Fn, const _Tp&>; - static_assert(__expected::__is_expected<_Up>); - static_assert(is_same_v); + static_assert(__expected::__is_expected<_Up>, + "the function passed to std::expected::and_then " + "must return a std::expected"); + static_assert(is_same_v, + "the function passed to std::expected::and_then " + "must return a std::expected with the same error_type"); if (has_value()) return std::__invoke(std::forward<_Fn>(__f), _M_val); @@ -871,8 +879,12 @@ namespace __expected and_then(_Fn&& __f) && { using _Up = __expected::__result<_Fn, _Tp&&>; - static_assert(__expected::__is_expected<_Up>); - static_assert(is_same_v); + static_assert(__expected::__is_expected<_Up>, + "the function passed to std::expected::and_then " + "must return a std::expected"); + static_assert(is_same_v, + "the function passed to std::expected::and_then " + "must return a std::expected with the same error_type"); if (has_value()) return std::__invoke(std::forward<_Fn>(__f), std::move(_M_val)); @@ -886,8 +898,12 @@ namespace __expected and_then(_Fn&& __f) const && { using _Up = __expected::__result<_Fn, const _Tp&&>; - static_assert(__expected::__is_expected<_Up>); - static_assert(is_same_v); + static_assert(__expected::__is_expected<_Up>, + "the function passed to std::expected::and_then " + "must return a std::expected"); + static_assert(is_same_v, + "the function passed to std::expected::and_then " + "must return a std::expected with the same error_type"); if (has_value()) return std::__invoke(std::forward<_Fn>(__f), std::move(_M_val)); @@ -900,8 +916,12 @@ namespace __expected or_else(_Fn&& __f) & { using _Gr = __expected::__result<_Fn, _Er&>; - static_assert(__expected::__is_expected<_Gr>); - static_assert(is_same_v); + static_assert(__expected::__is_expected<_Gr>, + "the function passed to std::expected::or_else " + "must return a std::expected"); + static_assert(is_same_v, + "the function passed to std::expected::or_else " + "must return a std::expected with the same value_type"); if (has_value()) return _Gr(in_place, _M_val); @@ -914,8 +934,12 @@ namespace __expected or_else(_Fn&& __f) const & { using _Gr = __expected::__result<_Fn, const _Er&>; - static_assert(__expected::__is_expected<_Gr>); - static_assert(is_same_v); + static_assert(__expected::__is_expected<_Gr>, + "the function passed to std::expected::or_else " + "must return a std::expected"); + static_assert(is_same_v, + "the function passed to std::expected::or_else " + "must return a std::expected with the same value_type"); if (has_value()) return _Gr(in_place, _M_val); @@ -929,8 +953,12 @@ namespace __expected or_else(_Fn&& __f) && { using _Gr = __expected::__result<_Fn, _Er&&>; - static_assert(__expected::__is_expected<_Gr>); - static_assert(is_same_v); + static_assert(__expected::__is_expected<_Gr>, + "the function passed to std::expected::or_else " + "must return a std::expected"); + static_assert(is_same_v, + "the function passed to std::expected::or_else " + "must return a std::expected with the same value_type"); if (has_value()) return _Gr(in_place, std::move(_M_val)); @@ -943,8 +971,12 @@ namespace __expected or_else(_Fn&& __f) const && { using _Gr = __expected::__result<_Fn, const _Er&&>; - static_assert(__expected::__is_expected<_Gr>); - static_assert(is_same_v); + static_assert(__expected::__is_expected<_Gr>, + "the function passed to std::expected::or_else " + "must return a std::expected"); + static_assert(is_same_v, + "the function passed to std::expected::or_else " + "must return a std::expected with the same value_type"); if (has_value()) return _Gr(in_place, std::move(_M_val)); diff --git a/libstdc++-v3/include/std/optional b/libstdc++-v3/include/std/optional index 4f75eb96f977..53450c760d9f 100644 --- a/libstdc++-v3/include/std/optional +++ b/libstdc++-v3/include/std/optional @@ -1048,7 +1048,9 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION and_then(_Fn&& __f) & { using _Up = remove_cvref_t>; - static_assert(__is_optional_v>); + static_assert(__is_optional_v>, + "the function passed to std::optional::and_then " + "must return a std::optional"); if (has_value()) return std::__invoke(std::forward<_Fn>(__f), **this); else @@ -1060,7 +1062,9 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION and_then(_Fn&& __f) const & { using _Up = remove_cvref_t>; - static_assert(__is_optional_v<_Up>); + static_assert(__is_optional_v<_Up>, + "the function passed to std::optional::and_then " + "must return a std::optional"); if (has_value()) return std::__invoke(std::forward<_Fn>(__f), **this); else @@ -1072,7 +1076,9 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION and_then(_Fn&& __f) && { using _Up = remove_cvref_t>; - static_assert(__is_optional_v>); + static_assert(__is_optional_v>, + "the function passed to std::optional::and_then " + "must return a std::optional"); if (has_value()) return std::__invoke(std::forward<_Fn>(__f), std::move(**this)); else @@ -1084,7 +1090,9 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION and_then(_Fn&& __f) const && { using _Up = remove_cvref_t>; - static_assert(__is_optional_v>); + static_assert(__is_optional_v>, + "the function passed to std::optional::and_then " + "must return a std::optional"); if (has_value()) return std::__invoke(std::forward<_Fn>(__f), std::move(**this)); else @@ -1140,7 +1148,9 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION or_else(_Fn&& __f) const& { using _Up = invoke_result_t<_Fn>; - static_assert( is_same_v, optional> ); + static_assert(is_same_v, optional>, + "the function passed to std::optional::or_else " + "must return a std::optional"); if (has_value()) return *this; @@ -1153,7 +1163,9 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION or_else(_Fn&& __f) && { using _Up = invoke_result_t<_Fn>; - static_assert( is_same_v, optional> ); + static_assert(is_same_v, optional>, + "the function passed to std::optional::or_else " + "must return a std::optional"); if (has_value()) return std::move(*this); -- 2.43.5