Search code examples
c++static-assert

Comparing static field pointers at compile time

I have a class B deriving from class A. A declares a static field f, and B might declare a similar field of the same name. The following does not work:

struct A { static int f; };
struct B : A { static int f; }; // A::f is different from B::f
struct C : A {}; // A::f is the same as C::f
BOOST_STATIC_ASSERT((&A::f != &B::f));
BOOST_STATIC_ASSERT((&A::f == &C::f));

Even though theoretically those assertions could be checked at compile time, they are disallowed since constant expressions cannot take addresses.

Is there a way to make this kind of check work at compile time?

Solution

  • Try putting the definitions of the static variables in scope of the static asserts.

    This works fine with gcc 4.7.2:

    struct A { static int f; };
struct B : A { static int f; };
struct C : A {};

int A::f;
int B::f;

static_assert(&A::f != &B::f, "B");
static_assert(&A::f == &C::f, "C");

int main()
{
}

    Compile with:

    $ g++ -std=gnu++11 test.cpp
$ ./a.out