#include <sigc++/sigc++.h>

void f(sigc::slot<void()> s) {}
void f(sigc::slot<void(int)> s) {}

class A {
   void test() {
      f(sigc::mem_fun(*this, &A::test));
   }
};

a.cpp: In member function ‘void A::test()’:
a.cpp:8:39: error: call of overloaded ‘f(sigc::bound_mem_functor<void (A::*)()>)’ is ambiguous
    8 |       f(sigc::mem_fun(*this, &A::test));
      |                                       ^
a.cpp:3:6: note: candidate: ‘void f(sigc::slot<void()>)’
    3 | void f(sigc::slot<void()> s) {}
      |      ^
a.cpp:4:6: note: candidate: ‘void f(sigc::slot<void(int)>)’
    4 | void f(sigc::slot<void(int)> s) {}
      |