template <class T1, class T2, class T3>
T3 func(T1, T2)
{
...
}

template <typename T1, typename T2, typename T3>
T1 func(T3, T2)
{
...
}

template <class T1, T2, class T3>
T2 func(T1, T3)
{
...
}

template <class T>
T func(T, T)
{
...
}

template <typename T, typename T>
T func(T, T)
{
...
}

template <class T, int sz>
T func(const T (&arr)[sz])
{
...
}

template <class T1, typename T2, class T3>
T1 func(T2, T3)
{
...
}