VS2010的解决方法：模板和重载函数

Question

I've code that are perfect build with mingw/g++ compilers but MSVC (2010) encountered error. Problem is overloaded functions and templates. May be somebody know workaround for MSVC? If workaround not exist (proof link is diserable) it also answer.

Code example:

#include <iostream>

struct Function 
{
    virtual ~Function() {}
    virtual void operator()() = 0;
};

template <typename Class, typename ARG1>
struct MemberFunction1 : public Function
{
    typedef void (Class::*MEM_FUNC)(ARG1);
    explicit MemberFunction1(Class * obj, MEM_FUNC func, ARG1 arg1) :  m_object(obj), m_func(func), m_arg1(arg1) {}

    virtual void operator()()
    {
        (m_object->*m_func)(m_arg1);
    }

    Class *  m_object;
    MEM_FUNC m_func;    
    ARG1     m_arg1;
};

struct FunctionStorage
{
    explicit FunctionStorage(Function * func) : m_func(func) {}

    virtual ~FunctionStorage()
    {
        if (m_func)
        {
            delete m_func;
            m_func = 0;
        }
    }

    void call() { (*m_func)(); }
    Function * m_func;
};

struct MemberFunction : public FunctionStorage
{
    template <typename Class, typename ARG1>
    MemberFunction(Class * obj, void (Class::*func)(ARG1), ARG1 arg1) : FunctionStorage(new MemberFunction1<Class, ARG1>(obj, func, arg1)) {}
};


class Foo 
{
public:
    void funcWithParam(int value)
    {
        std::cout << "foo::funcWithParam(" << value << ")\n";
    }
    void funcWithParam(const char * msg)
    {
        std::cout << "foo::funcWithParam(" << msg << ")\n";
    }
};

int main()
{
    Foo f;    
    MemberFunction(&f, &Foo::funcWithParam, 5).call(); // problem here, if remove one of funcWithParam (stay only 1 function, no overload) all will be ok
    MemberFunction(&f, &Foo::funcWithParam, "hello").call(); 
    return 0;
}

My output:

main.cpp(65): error C2660: 'MemberFunction::MemberFunction' : function does not take 3 arguments
main.cpp(65): error C2228: left of '.call' must have class/struct/union
main.cpp(66): error C2660: 'MemberFunction::MemberFunction' : function does not take 3 arguments
main.cpp(66): error C2228: left of '.call' must have class/struct/union

Here is ideone build result.

Answer 1

Both overloads of Foo::funcWithParam match void (Class::*func)(ARG1) in MemberFunction(Class * obj, void (Class::*func)(ARG1), ARG1 arg1) , so the second parameter type is ambiguous: the compiler can't decide whether ARG1 is int or const char * .

Funny thing is if you invert the order of parameters in your templated constructor, ie make it like this: MemberFunction(Class * obj, ARG1 arg1, void (Class::*func)(ARG1) ) and also change your call site to this: MemberFunction(&f, 5, &Foo::funcWithParam) it will work. The compiler first encounters the second parameter from which it deduces the type ARG1 is int . It then proceeds to the third parameter and because it now knows ARG1 is int , it knows which overload of &Foo::funcWithParam to select.

I am not sure what the behavior the standard dictates should be in this case, but one of the compilers surely has a bug, most likely VS2010.