C ++可变参数模板以评估指向成员的指针

Question

I would like to create a variadic template that evaluates nested pointer to members. I have tried the following:

template<typename T, typename U, typename... V>
auto getField(T &input, U (T::*field), V... args)
    -> decltype(getField(input.*field, &args...))
{
    getField(input.*field, &args...);
}

template<typename T, typename U>
U getField(T &input, U (T::*field))
{
    return input.*field;
}

struct inner {
    int val;
};

struct outer {
    inner in;
};

void main() {
    outer p{{5}};
    cout << getField(p, &outer::in, &inner::val) << endl;
}

When I compile the above in VS, I get the following error messages:

error C2672: 'getField': no matching overloaded function found
error C2893: Failed to specialize function template 'unknown-type getField(T &, UT::* ,V...)'
note: With the following template arguments:
note: 'T=outer'
note: 'U=outer::inner'
note: 'V={int outer::inner::* }'

How can I fix the above variadic template to compile, and return p.in.val ? Note that my compiler doesn't support auto template parameters.

Answer 1

Change order of methods and fix "typos":

template<typename T, typename U>
U getField(T &input, U (T::*field))
{
    return input.*field;
}

template<typename T, typename U, typename... V>
auto getField(T &input, U (T::*field), V... args)
    -> decltype(getField(input.*field, args...))
{
    return getField(input.*field, args...);
}

Demo