Re: extending c++ classes and enumerations
Al skrev:
Hi there!
alex wrote:
// enum.h:
enum ThreadState { ERROR = -1, RUNNING, TERMINATED };
void PrintState(ThreadState state) {
switch (state) {
case ERROR: cout << "Error"; break;
case RUNNING: cout << "Running"; break;
case TERMINATED: cout << "Terminated"; break;
default: throw exception("Invalid State.");
}
}
// enum2.h:
extend enum ThreadState { CANCELLED };
int main() {
PrintState(CANCELLED); // Prints or throws or what?
return 0;
}
Well, in this case an exception is thrown. :-)
I've noticed that the GNU implementation of standard C++ headers ios
uses static members for e.g. the open mode. In the thread example, this
would look like
enum _ThreadState { _ERROR = -1, _RUNNING, _TERMINATED };
const static int ERROR = _ERROR;
const static int RUNNING = _RUNNING;
const static int TERMINATED = _TERMINATED;
// enum2.h
enum _ThreadState_Cancelled { _CANCELLED };
const static int CANCELLED = _CANCELLED;
but then the point of using enums vanish (no compile checking).
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