Unable to call my operator<T t>() if it doesn't receives arguments

I’m trying to create a State class that will be used like an enum.

template <class ApplicationType>
class State
{
public:

     
    template<class T>
    requires requires(){ std::is_base_of<ApplicationType, T>::value; }
    unsigned int operator()()   //broken operator
    {
        static unsigned int localCounter = counter++;
        return localCounter;
    }

    template<class T>
    requires requires(){ std::is_base_of<ApplicationType, T>::value; }
    unsigned int operator()(T t)   //working operator
    {
        static unsigned int localCounter = counter++;
        return localCounter;
    }

private:
    unsigned int counter = 0;
};

My problem is that when I call the first operator State::operator()() the code doesn’t compile, but when I call the second one State::operator()(T t) everything works fine.

class Base{};

class Derived: Base{};


int main()
{
    State<Base> myState;
    Derived d;

    myState<Derived>(); // Error
    myState(d);         // OK

    return 0;
}

Error message:
expected primary-expression before ‘>’ token
expected primary-expression before ‘)’ token

PS: I’m using G++ with -std=c++20

>Solution :

Just use the explicit notation for the call:

myState.operator()<Derived>();