使用可变参数模板的类成员函数继承

Question

In the following code it seems that the variadic template version of Container doesn't inherit the name function of the single template version of Container, g++ 4.5.2 complains:

no matching function for call to ”Container<Variable1, Variable2>::name(Variable2)”
candidate is: std::string Container<First_Variable, Rest ...>::name(First_Variable) [with First_Variable = Variable1, Rest = {Variable2}, std::string = std::basic_string<char>]

The code:

#include "iostream"
#include "string"

using namespace std;

struct Variable1 {
    string operator()() {
        return string("var1");
    }
};

struct Variable2 {
    string operator()() {
        return string("var2");
    }
};

template<class... T> class Container;

template<class First_Variable, class... Rest>
class Container<First_Variable, Rest...> : public Container<Rest...> {
public:
    string name(First_Variable variable) {
        return variable();
    }
};

template<class Variable> class Container<Variable> {
public:
    string name(Variable variable) {
        return variable();
    }
};

int main(void) {
    Container<Variable1, Variable2> c;
    cout << "Variables in container: " << c.name(Variable1()) << ", " << c.name(Variable2()) << endl;
    return 0;
}

What am I doing wrong or is this even supposed to work?

Answer 1

The name are hiding the name of the base class. Try

template<class... T> class Container;

template<class First_Variable, class... Rest>
class Container<First_Variable, Rest...> : public Container<Rest...> {
public:
    using Container<Rest...>::name;

    string name(First_Variable variable) {
        return variable();
    }
};

template<class Variable> class Container<Variable> {
public:
    string name(Variable variable) {
        return variable();
    }
};

If you are pedantic, then your partial specializations are incorrect. The C++11 spec terms ambiguous two partial specializations of the form <FixedParameter, Pack...> and <FixedParameter> . This was discussed and many people find it surprising, so some compilers do not implement that part of C++11.