Question

Would someone kindly tell me why the complier flags an error when I attempt to call the versions of the member function Foo<T>::setValue that involve more than 1 template argument, as shown below.

See ideone

class Bar
{
public:
    enum TYPE{};
};

//////////////////////////////////////////////////////////////////////////////////////

template<typename T>
class Foo
{
public:
    template<typename P>
    void setValue1();

    template<typename P, int>
    void setValue2();

    template<typename P, typename P::TYPE>
    void setValue3();

private:
    T   m_value;
};

//////////////////////////////////////////////////////////////////////////////////////

template<typename T>
template<typename P>
void Foo<T>::setValue1()
{
}

template<typename T>
template<typename P, int>
void Foo<T>::setValue2()
{
}

template<typename T>
template<typename P, typename P::TYPE>
void Foo<T>::setValue3()
{
}

//////////////////////////////////////////////////////////////////////////////////////

int main()
{
    Foo<Bar::TYPE> f1;

    f1.setValue1<Bar>();                // Compiles
    f1.setValue2<Bar, int>();       // ERROR
    f1.setValue3<Bar, Bar::TYPE>(); // ERROR

    return EXIT_SUCCESS;
}

GCC error:

error: no matching function for call to ‘Foo<Bar::TYPE>::setValue2()’
error: no matching function for call to ‘Foo<Bar::TYPE>::setValue3()’

MSVC .NET 2008 error:

Test6.cpp(60) : error C2975: 'Foo<T>::setValue2' : invalid template argument for 'unnamed-parameter', expected compile-time constant expression
        with
        [
            T=Bar::TYPE
        ]
        Test6.cpp(24) : see declaration of 'Foo<T>::setValue2'
        with
        [
            T=Bar::TYPE
        ]
Test6.cpp(61) : error C2975: 'Foo<T>::setValue3' : invalid template argument for 'unnamed-parameter', expected compile-time constant expression
        with
        [
            T=Bar::TYPE
        ]
        Test6.cpp(27) : see declaration of 'Foo<T>::setValue3'
        with
        [
            T=Bar::TYPE
        ]   

Answer 1

I addition to the problem @Jason mentioned, your second function template takes an int as its second argument, and you are providing a type.

This was fixed by changing the name to setValue2 per @Jason’s post, then changing the function call to:

f1.setValue2<Bar, 3>();        

I’m not sure what you’re trying to accomplish with the third template function definition. It seems you should only need one template argument, since P::Type can also be derived.

I should also note that your class definition is not really precise — the class’s template argument is a typename, but you’re passing it Bar::TYPE which is an enum type.