PR libstdc++/90246
* include/std/variant (holds_alternative, get, get_if): Improve
static assertion messages.
(bad_variant_access::bad_variant_access()): Change default message.
(__throw_bad_variant_access(bool)): New overload.
(get): Use new overload.
(visit, visit<R>): Improve exception message.
Tested x86_64-linux, committed to trunk.
commit dfb7731e63f19549ba31e3b89dc0ec63a3f3119e
Author: Jonathan Wakely <jwak...@redhat.com>
Date: Thu Apr 25 17:20:26 2019 +0100
PR libstdc++/90246 Improve text of std::variant exceptions and assertions
PR libstdc++/90246
* include/std/variant (holds_alternative, get, get_if): Improve
static assertion messages.
(bad_variant_access::bad_variant_access()): Change default message.
(__throw_bad_variant_access(bool)): New overload.
(get): Use new overload.
(visit, visit<R>): Improve exception message.
diff --git a/libstdc++-v3/include/std/variant b/libstdc++-v3/include/std/variant
index eec41750da7..60472b4c799 100644
--- a/libstdc++-v3/include/std/variant
+++ b/libstdc++-v3/include/std/variant
@@ -1065,7 +1065,7 @@ namespace __variant
holds_alternative(const variant<_Types...>& __v) noexcept
{
static_assert(__detail::__variant::__exactly_once<_Tp, _Types...>,
- "T should occur for exactly once in alternatives");
+ "T must occur exactly once in alternatives");
return __v.index() == __detail::__variant::__index_of_v<_Tp, _Types...>;
}
@@ -1073,7 +1073,7 @@ namespace __variant
constexpr _Tp& get(variant<_Types...>& __v)
{
static_assert(__detail::__variant::__exactly_once<_Tp, _Types...>,
- "T should occur for exactly once in alternatives");
+ "T must occur exactly once in alternatives");
static_assert(!is_void_v<_Tp>, "_Tp should not be void");
return std::get<__detail::__variant::__index_of_v<_Tp, _Types...>>(__v);
}
@@ -1082,7 +1082,7 @@ namespace __variant
constexpr _Tp&& get(variant<_Types...>&& __v)
{
static_assert(__detail::__variant::__exactly_once<_Tp, _Types...>,
- "T should occur for exactly once in alternatives");
+ "T must occur exactly once in alternatives");
static_assert(!is_void_v<_Tp>, "_Tp should not be void");
return std::get<__detail::__variant::__index_of_v<_Tp, _Types...>>(
std::move(__v));
@@ -1092,7 +1092,7 @@ namespace __variant
constexpr const _Tp& get(const variant<_Types...>& __v)
{
static_assert(__detail::__variant::__exactly_once<_Tp, _Types...>,
- "T should occur for exactly once in alternatives");
+ "T must occur exactly once in alternatives");
static_assert(!is_void_v<_Tp>, "_Tp should not be void");
return std::get<__detail::__variant::__index_of_v<_Tp, _Types...>>(__v);
}
@@ -1101,7 +1101,7 @@ namespace __variant
constexpr const _Tp&& get(const variant<_Types...>&& __v)
{
static_assert(__detail::__variant::__exactly_once<_Tp, _Types...>,
- "T should occur for exactly once in alternatives");
+ "T must occur exactly once in alternatives");
static_assert(!is_void_v<_Tp>, "_Tp should not be void");
return std::get<__detail::__variant::__index_of_v<_Tp, _Types...>>(
std::move(__v));
@@ -1139,7 +1139,7 @@ namespace __variant
get_if(variant<_Types...>* __ptr) noexcept
{
static_assert(__detail::__variant::__exactly_once<_Tp, _Types...>,
- "T should occur for exactly once in alternatives");
+ "T must occur exactly once in alternatives");
static_assert(!is_void_v<_Tp>, "_Tp should not be void");
return std::get_if<__detail::__variant::__index_of_v<_Tp, _Types...>>(
__ptr);
@@ -1150,7 +1150,7 @@ namespace __variant
get_if(const variant<_Types...>* __ptr) noexcept
{
static_assert(__detail::__variant::__exactly_once<_Tp, _Types...>,
- "T should occur for exactly once in alternatives");
+ "T must occur exactly once in alternatives");
static_assert(!is_void_v<_Tp>, "_Tp should not be void");
return std::get_if<__detail::__variant::__index_of_v<_Tp, _Types...>>(
__ptr);
@@ -1213,22 +1213,34 @@ namespace __variant
class bad_variant_access : public exception
{
public:
- bad_variant_access() noexcept : _M_reason("Unknown reason") { }
+ bad_variant_access() noexcept { }
+
const char* what() const noexcept override
{ return _M_reason; }
private:
- bad_variant_access(const char* __reason) : _M_reason(__reason) { }
+ bad_variant_access(const char* __reason) noexcept : _M_reason(__reason) { }
- const char* _M_reason;
+ // Must point to a string with static storage duration:
+ const char* _M_reason = "bad variant access";
friend void __throw_bad_variant_access(const char* __what);
};
+ // Must only be called with a string literal
inline void
__throw_bad_variant_access(const char* __what)
{ _GLIBCXX_THROW_OR_ABORT(bad_variant_access(__what)); }
+ inline void
+ __throw_bad_variant_access(bool __valueless)
+ {
+ if (__valueless) [[__unlikely__]]
+ __throw_bad_variant_access("std::get: variant is valueless");
+ else
+ __throw_bad_variant_access("std::get: wrong index for variant");
+ }
+
template<typename... _Types>
class variant
: private __detail::__variant::_Variant_base<_Types...>,
@@ -1592,7 +1604,7 @@ namespace __variant
static_assert(_Np < sizeof...(_Types),
"The index should be in [0, number of alternatives)");
if (__v.index() != _Np)
- __throw_bad_variant_access("Unexpected index");
+ __throw_bad_variant_access(__v.valueless_by_exception());
return __detail::__variant::__get<_Np>(__v);
}
@@ -1603,7 +1615,7 @@ namespace __variant
static_assert(_Np < sizeof...(_Types),
"The index should be in [0, number of alternatives)");
if (__v.index() != _Np)
- __throw_bad_variant_access("Unexpected index");
+ __throw_bad_variant_access(__v.valueless_by_exception());
return __detail::__variant::__get<_Np>(std::move(__v));
}
@@ -1614,7 +1626,7 @@ namespace __variant
static_assert(_Np < sizeof...(_Types),
"The index should be in [0, number of alternatives)");
if (__v.index() != _Np)
- __throw_bad_variant_access("Unexpected index");
+ __throw_bad_variant_access(__v.valueless_by_exception());
return __detail::__variant::__get<_Np>(__v);
}
@@ -1625,7 +1637,7 @@ namespace __variant
static_assert(_Np < sizeof...(_Types),
"The index should be in [0, number of alternatives)");
if (__v.index() != _Np)
- __throw_bad_variant_access("Unexpected index");
+ __throw_bad_variant_access(__v.valueless_by_exception());
return __detail::__variant::__get<_Np>(std::move(__v));
}
@@ -1646,7 +1658,7 @@ namespace __variant
visit(_Visitor&& __visitor, _Variants&&... __variants)
{
if ((__variants.valueless_by_exception() || ...))
- __throw_bad_variant_access("Unexpected index");
+ __throw_bad_variant_access("std::visit: variant is valueless");
using _Result_type = std::invoke_result_t<_Visitor,
decltype(std::get<0>(std::declval<_Variants>()))...>;
@@ -1663,7 +1675,7 @@ namespace __variant
visit(_Visitor&& __visitor, _Variants&&... __variants)
{
if ((__variants.valueless_by_exception() || ...))
- __throw_bad_variant_access("Unexpected index");
+ __throw_bad_variant_access("std::visit<R>: variant is valueless");
return std::__do_visit<_Res>(std::forward<_Visitor>(__visitor),
std::forward<_Variants>(__variants)...);
