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libstdc++: Fix visitor return type diagnostics [PR97449]

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libstdc++-v3/ChangeLog:

	PR libstdc++/97449
	* include/std/variant
	(__gen_vtable_impl<>::_S_apply_single_alt):
	Diagnose visitor return type mismatches here..
	(__gen_vtable_impl</*base case*/>::_S_apply):
	..not here.
This commit is contained in:
Ville Voutilainen 2020-10-17 22:08:50 +03:00
parent f476a9fe91
commit 1f65bf2aa6
1 changed files with 7 additions and 5 deletions
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12
libstdc++-v3/include/std/variant
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@ -960,9 +960,13 @@ namespace __variant
}
else
{
__element = __gen_vtable_impl<
auto __tmp_element = __gen_vtable_impl<
remove_reference_t<decltype(__element)>,
std::index_sequence<__indices..., __index>>::_S_apply();
static_assert(is_same_v<_Tp, decltype(__tmp_element)>,
"std::visit requires the visitor to have the same "
"return type for all alternatives of a variant");
__element = __tmp_element;
}
}
};
@ -1026,10 +1030,8 @@ namespace __variant
std::declval<_Variants>()...))>;
if constexpr (__visit_ret_type_mismatch)
{
static_assert(!__visit_ret_type_mismatch,
"std::visit requires the visitor to have the same "
"return type for all alternatives of a variant");
return __nonesuch{};
struct __cannot_match {};
return __cannot_match{};
}
else
return _Array_type{&__visit_invoke};