I recently updated my sigs project (simple thread-safe signal/slot C++ library) with support for ambiguous member functions by use of the sigs::Use<>::overloadOf():
template <typename... Args>
struct Use {
template <typename Cls, typename Ret>
static auto overloadOf(Ret (Cls::*MembFunc)(Args...)) {
return MembFunc;
}
};
It makes use of variadic templates and auto return type deduction so the compiler must be C++14 compliant.
To illustrate why it was needed consider this: Sometimes there are several overloads for a given function and then it’s not enough to just specify &Class::functionName because the compiler does not know which overload to choose.
The Ambiguous class has two overloads of foo:
class Ambiguous {
public:
void foo(int i, int j) { std::cout << "Ambiguous::foo(int, int)\n"; }
void foo(int i, float j) { std::cout << "Ambiguous::foo(int, float)\n"; }
};
Without the new construct the following would result in compilation failure:
sigs::Signal<void(int, int)> s;
Ambiguous amb;
s.connect(&amb, &Ambiguous::foo); // <-- Will fail!
The error would look something similar to this:
test.cc:147:7: error: no matching member function for call to 'connect'
s.connect(&amb, &Ambiguous::foo);
~~^~~~~~~
./sigs.h:144:16: note: candidate template ignored: couldn't infer template argument 'MembFunc'
Connection connect(Instance *instance, MembFunc Instance::*mf) {
To fix it we must use sigs::Use<>::overloadOf():
s.connect(&amb, sigs::Use<int, int>::overloadOf(&Ambiguous::foo));
s(42, 48);
/* Prints:
Ambiguous::foo(int, int)
*/
Without changing the signal we can also connect the second overload foo(int, float):
// This one only works because int can be coerced into float!
s.connect(&amb, sigs::Use<int, float>::overloadOf(&Ambiguous::foo));
s(12, 34);
/* Prints:
Ambiguous::foo(int, int)
Ambiguous::foo(int, float)
*/