https://gcc.gnu.org/bugzilla/show_bug.cgi?id=91541
Bug ID: 91541
Summary: [C++17] Exception specification of operator= of
node-based containers may be broken
Product: gcc
Version: 9.1.0
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: libstdc++
Assignee: unassigned at gcc dot gnu.org
Reporter: frankhb1989 at gmail dot com
Target Milestone: ---
Case:
#include <utility>
#include <memory_resource>
#include <map>
#include <functional>
struct A : std::allocator<std::pair<const int, int>>
{
template<typename U>
struct rebind
{
using other = std::pmr::polymorphic_allocator<U>;
};
};
int main()
{
using always_equal = std::allocator_traits<A>::is_always_equal;
using C = std::less<>;
constexpr bool std_nothrow = always_equal::value &&
std::is_nothrow_move_assignable_v<C>;
static_assert(std_nothrow);
static_assert(!(std_nothrow &&
!std::is_nothrow_move_assignable<std::map<int, int, C, A>>::value));
}
The defaulted exception specification is from _Rb_tree which uses node
allocator traits instead of the allocator_traits<value_type>, so
is_always_equal::value can differ than expected.
There is a similar problem in list/forward_list::operator='s implementations:
they use the node allocator_traits explicitly, not the required exception
specification by the standard.
