Why does overload ! operator need a const return

Question

g++ 4.5.3 (cygwin)

class SlipDatum {
public:
   bool operator!();
   long operator~();
}

bool SlipDatum::operator!() { }
long SlipDatum::operator~() { }

Operator!() expects prototype: const bool operator!();

but operator~() works with no expectations. Any reaon why?

The compiler error is:

SlipDatum.cpp:104:15: error: prototype for 'const slip::BOOL slip::SlipDatum::operator!()' does not match any in class 'slip::SlipDatum' SlipDatum.h:15295:18: error: candidate is: bool slip::SlipDatum::operator!()

Answer 1

It is hard to figure out what you mean exactly, but in many cases missing ; after class definition can lead to various bizarre and confusing error messages. I can't reproduce yours though in my version of GCC.

Anyway, add a ; at the end of class definition.

Answer 2

class SlipDatum {
public:
   bool operator!();
   long operator~();
};

bool SlipDatum::operator!() { return false; }
long SlipDatum::operator~() { return 0; }

int main() {
  SlipDatum unused;
}

this code compiles fine in gcc 4.3.4 gcc 4.5.1 and gcc 4.7.2

Either you found a strange bug in gcc 4.5.3 (cygwin), or your problem is you failed to actually return from a function that expects a return value, or your question is badly formed, or your error is otherwise in the difference between your post and my answer.