How can I make compile time assertions without C++11

Question

In a job interview, I was asked to write a metafunction that determined whether a type was a pointer. This is what I presented:

template 
struc         


        

Answer 1

I would use BOOST_STATIC_ASSERT. You can look at the code: boost/static_assert.hpp.

Here's a very simplified version, just to give you an idea:

#define JOIN(X, Y) DO_JOIN(X, Y)
#define DO_JOIN(X, Y) X ## Y

template
struct Static_assert_helper;  // incomplete type

template<>
struct Static_assert_helper {
    typedef int Type;
};

#define STATIC_ASSERT(cond) \
    typedef Static_assert_helper<(cond)>::Type JOIN(Static_assert_typedef_, __LINE__)

It can be used in many places (see the documentation for examples).

(Boost's implementation is more complete, with e.g. a sizeof and an intermediate struct, to give a better error message and be portable on a wide range of compilers.)