How to fix the syntax in this code rife with templates?

Question

The following code

template<typename T, typename U> class Alpha
{
public:
    template<typename V> void foo() {}
};

template<typename T, typename U> class Beta
{
public:
    Alpha<T, U> alpha;
    void arf();
};

template<typename T, typename U> void Beta<T, U>::arf()
{
    alpha.foo<int>();
}

int main()
{
    Beta<int, float> beta;
    beta.arf();
    return 0;
}

Fails to compile due to:

../src/main.cpp: In member function ‘void Beta::arf()’:
../src/main.cpp:16: error: expected primary-expression before ‘int’
../src/main.cpp:16: error: expected ‘;’ before ‘int’

How the heck do I fix this? I've tried everything I can think of.

Answer 1

Try alpha.template foo<int>(). Note that your code compiles fine with VC8. Since alpha is of dependant type, you have to specify that foo is a template.

Answer 2

alpha::foo is a dependent name, use alpha.template foo<int>().

Dependent names are assumed to

• not be types unless prefixed by typename
• not be templates unless directly prefixed by template