ambiguous function call

gistfile1.c

void testo(
    std::function<void(std::string str, int len)> a,
    std::function<void(int i)> b
) {

}

void testo(
    std::function<void(int i)> a,
    std::function<void(std::string str, int len)> b
) {

}

// error, ambiguous call to overload function
testo(
    [](int i) {},
    [](std::string str, int len) {}
);