C++ Variable declarable in function body, but not class member?

Question

I want to create a C++ class with the following type:

1. It can be declared inside of a function.
2. It can be declared inside of a member function.
3. It can not be declared as a class member.

The use of this: think "Root" objects for a GC.

Is this possible in C++? In particular, I'm using g++. Willing to switch to clang. Either templates or macro solution fine.

Thanks!

Answer 1

You could do it with a macro, perhaps:

#define MY_TYPE \
    do { } while(0); \
    RealType

void foo() {
    MY_TYPE myvar;
    myvar.Whatever();
}

This would only compile inside a function (because of the "do ... while" bit - though you'd get a really weird error message). It seems like one of those "evil" uses of macros that you would want to avoid, however...