#define TYPE_CHECK(T, S) \
while (false) { \
*(static_cast<T* volatile*>(0)) = static_cast<S*>(0); \
}
I am reading Google v8's code and found the above macro for type check.
However, I do not understand why it works. while(false) never get executed, right? Can someone explain those lines? Thanks
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.