static_assert on inline function gives error

Question

Consider the following case

typedef void (*foo)();
template<foo f>
struct bar {
     static_assert(f!=nullptr,"f == null!");
};

void baz() {}
inline void bax() {  }

bar<baz> ok;
bar<bax> bad; // error: non-constant condition for static assertion

Both baz and bax are accepted as template arguments. It indicates that both are accepted as constants. However, at static_assert they appears to be different (at least in gcc 4.9) - bax is not a constant anymore.

My assumption was that static_assert and template evaluate constantness identically. E.g. either error should be

• 'bax is not a valid template argument' or
• static_assert should not raise non-constant condition error.

Am I wrong?

Answer 1

When a function is inlined, the pointer to the function does not exist. So we can not compare it with nullptr.

Whether a function is eventually inlined or not, depends on the compiler. inline keyword does not guarantee that.