How does the following code work?

Question

    #define TYPE_CHECK(T, S)                                     \\
    while (false) {                                              \\
      *(static_cast

        

Answer 1

Yes, but the compiler still performs syntax & semantic checks on the loop contents. So if something is wrong (i.e. the implicit type conversion from S* to T* is illegal, which happens if T is neither S nor a base class of S), compilation fails. Otherwise, the quality of the resulting machine code is not affected since the optimizer will detect the nonreachable code and remove it silently.