can I use SFINAE to selectively define a member variable in a template class?

Question

So what I want to do is to create a template class which may or may not contain a member variable based on the template argument passed in. like following:

t         


        

Answer 1

I have a workaround for this. Probably looks ugly but does resolve some of my issues

First I define a type with zero size:

typedef int zero[0];

Next I create a macro:

#ifndef VAR

#define VAR(Enable,YourType,VarName) \    

std::conditional< Enable,YourType,zero >::type VarName

#endif

Then a class like this:

template < int Cond >
class Foo
{
    VAR(Cond == 0,int,var);

    void print()
    {
        if (!sizeof(var)) return;
        //...
    }
};

When you are using a result like var, check the size of it before using it. If the size is zero, it is invalid.