https://gcc.gnu.org/bugzilla/show_bug.cgi?id=111568
Bug ID: 111568
Summary: std::not_fn can accept non-movable function
Product: gcc
Version: 14.0
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: libstdc++
Assignee: unassigned at gcc dot gnu.org
Reporter: hewillk at gmail dot com
Target Milestone: ---
It seems that std::not_fn should reject the following code according to
[func.not.fn]: "Mandates: is_constructible_v<FD, F> &&
is_move_constructible_v<FD> is true."
https://godbolt.org/z/MsrqnbY74
#include <functional>
struct OnlyCopyableFun {
OnlyCopyableFun() = default;
OnlyCopyableFun(const OnlyCopyableFun&) = default;
OnlyCopyableFun(OnlyCopyableFun&&) = delete;
bool operator()(auto) const;
};
int main() {
OnlyCopyableFun f;
auto nf = std::not_fn(f); // only ill-formed in libc++
}
Not quite sure why these standard call wrapper factories (std::bind_front,
std::bind, etc.) require all argument types to be move-constructible, although
the call wrapper produced in the above example is still move-constructible as
its underlying type has a copy constructor.
It seems to me that just requiring is_constructible_v<FD, F> is enough, which
is what the range adaptor object does.
