Question

Let’s say I have 3 classes. I expect sizeof() each class to be exactly the same–say 512 bytes.

How can I use something like BOOST_STATIC_ASSERT to apply to all of them such that

1. I only need to use BOOST_STATIC_ASSERT in a single place (DRY principle)
2. Evaluated once at compile-time and not run-time

Note: we can use whatever C++ techniques we want (create more class , use inheritance, etc)

My naive solution is presented below:

class A { ...stuff }; BOOST_STATIC_ASSERT( sizeof(A) == 512 );
class B { ...stuff }; BOOST_STATIC_ASSERT( sizeof(B) == 512 );
class C { ...stuff }; BOOST_STATIC_ASSERT( sizeof(C) == 512 );

Answer 1

This seems to work with gcc 4.0.1 and boost 1.39:

template <typename T, size_t S>
struct enforce_size
{
    enforce_size()
    {
        BOOST_STATIC_ASSERT( sizeof( T ) == S );
    }
};

class A: enforce_size<A,512> { /* stuff */ };