C++ Template Problem

[camelCase]

All right, so it's been a long time since I used C++.. And even longer since I used templates. I understand that I may be using templates in a weird way, if you'll look at the two bits of code below, but I assure you that I have a valid reason for doing so =P

I encountered a problem and decided to reduce my code to the simplest form that produces the error. Here are the results.

This compiles:

template <class T>
class Bar {};
 
template<class T, class Dummy=void>
class Foo;
 
template<class T>
class Foo <T, typename std::enable_if<
    std::is_base_of<Bar<T>, T>::value
>::type> {
    public:
        //THIS CHANGES IN THE 2ND SNIPPET
        void test () const {
            std::cout << "test";
        }
};
 
class Cat : Bar<Cat> {};
 
int main () {
    Foo<Cat> foo;
    foo.test();
    return 0;
}

This errors:

template <class T>
class Bar {};
 
template<class T, class Dummy=void>
class Foo;
 
template<class T>
class Foo <T, typename std::enable_if<
    std::is_base_of<Bar<T>, T>::value
>::type> {
    public:
        //THIS CHANGED!
        void test () const;
};
 
//THIS WAS ADDED SINCE THE 1ST SNIPPET!
template<class T>
void Foo<T>::test () const {
    std::cout << "test";
} //error C2039: 'test' : is not a member of 'Foo<T>'
 
class Cat : Bar<Cat> {};
 
int main () {
    Foo<Cat> foo;
    foo.test();
    return 0;
}

I have marked the differences. Why does it error in the 2nd code snippet? How do I keep declaration and definition separate while avoiding the error?

I'm guessing it's got something to do with this:
"template<class T>
void Foo<T>::test () const"

Like, this is the wrong way to tell the compiler that the method [ljass]test() const[/ljass] is a method of template class [ljass]template<class T>
class Foo <T, typename std::enable_if<
std::is_base_of<Bar<T>, T>::value
>::type>[/ljass]

 

[camelCase]

Oh, never mind. Got the answer. I'm supposed to define it like this..

template<class T>
void Foo<T, typename std::enable_if<
    std::is_base_of<Bar<T>, T>::value
>::type>::test () const {
    std::cout << "test";
}

You'll notice that the [ljass]std::enable_if<>[/ljass] from the class declaration also has to be in the method definitions.. Oh, gawd.. So verbose..

 

[s3rius]

Some call template metaprogramming the cancer of C++ =)

 

[camelCase]

Yes.. I can sort of see why..
But when it works, god, damn, it works.