In my view it is a bug. It gives an error that it can't find
std::throw, but that is gcc's problem, not the problem according to
the standard. According to the standard, the problem is that ::operator
new(size_t, nothrow_t) has not been declared. In fact, the relevant
paragraph of the standard never mentions std::nothrow . It only
mentions std::nothrow_t. Not the same thing.
In other words, this is an error message for developers, not for
users...i.e. a bug.
On 1/18/2025 3:18 PM, Andrew Pinski wrote:
On Sat, Jan 18, 2025 at 2:12 PM Lee Brown via Gcc <gcc@gcc.gnu.org> wrote:
Just to be clear, the appended 17 lines of very simple code breaks gcc
on every platform where <coroutine> header does not have <new> in its
include hierarchy....which I assume to be every platform.
See the discussion in the bug report:
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=95505 . That is there is
no bug in libstdc++ nor in GCC in theory. Any use of
get_return_object_on_allocation_failure for the promise_type requires
new to be included. Now there should be a note about a missing include
of new but that is just a small diagnostic issue.
Thanks,
Andrew Pinski
1) place code below in main.cpp
2) g++ -std=c++20 main.cpp
and you get
main.cxx: In function 'my_co do_co()':
main.cxx:16:7: error:
'my_co::promise_type::get_return_object_on_allocation_failure()' is
provided by 'std::__n4861::__coroutine_traits_impl<my_co,
void>::promise_type' {aka 'my_co::promise_type'} but *'std::nothrow'
cannot be found*
16 | my_co do_co() { co_return; }
| ^~~~~
Here's the code:
// begin code --------------------------------
#include <coroutine>
struct my_co {
struct promise_type {
static my_co get_return_object_on_allocation_failure() {
return my_co(); }
my_co get_return_object() { return my_co(); }
std::suspend_always initial_suspend() noexcept { return {}; }
std::suspend_always final_suspend() noexcept { return {}; }
void return_void() {}
void unhandled_exception() {}
};
};
my_co do_co() { co_return; }
int main()
{
do_co();
return 0;
}
// end code ----------------------------
