Taking the address of boost::hana::partial::operator()

Question

Suppose I have a lambda that does something:

auto thing = [](int x){ /* Stuff */ };

I want to save off the value "x" and call it later so I do:

auto other = boost::hana::partial(thing, 42);

Now, because I want to do some type erasure on this I want to take the address of the operator().....so I try to do this:

using type = decltype(other);
void (type::*ptr)(void) = &type::operator();

Clang complains, that the other object does not a sufficient function that matches the requirements: godbolt

It appears that the partial type is returning a reference (to void?)......why does this not work?

Answer 1

It (the operator()) has & const& && etc overloads; your member function pointer does not qualify *this by const or r/l value-ness. So does not match.

Add & or const& or && or const&& before = on the line that fails to compile, and it will compile.

Here is a [MCVE]:

struct foo {
    void bar()&{}
};

int main(){
    auto p = &foo::bar;
    void(foo::*p2)() = p; // lacks &
}